Muchas gracias y sorprendido por el tiempo de tu respuesta.
Hice lo que me indicás (abajo pego el los logos), y evidentemente el problema está en el Nod32, ya que después de haber hecho estos chequeos, desinstalé el Nod 32 y cargué una versión a prueba del Kaspersky, que si bien nunca lo había usado, "aparentemente" está funcionando el sistema mejor -espero que sea sólo eso-
Aquí van los logos:

KASPERSKY:

KASPERSKY ONLINE SCANNER REPORT
Saturday, July 01, 2006 11:40:31 AM
Operating System: Microsoft Windows XP Professional, Service Pack 2 (Build 2600)
Kaspersky Online Scanner version: 5.0.83.0
Kaspersky Anti-Virus database last update: 1/07/2006
Kaspersky Anti-Virus database records: 203951
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Scan Settings:
Scan using the following antivirus database: extended
Scan Archives: true
Scan Mail Bases: true

Scan Target - My Computer:
C:\
D:\

Scan Statistics:
Total number of scanned objects: 23520
Number of viruses found: 0
Number of infected objects: 0 / 0
Number of suspicious objects: 0
Duration of the scan process: 00:19:39

Infected Object Name / Virus Name / Last Action
C:\Documents and Settings\Administrator\Cookies\index.dat Object is locked skipped
C:\Documents and Settings\Administrator\Local Settings\Application Data\Microsoft\Windows\UsrClass.dat Object is locked skipped
C:\Documents and Settings\Administrator\Local Settings\Application Data\Microsoft\Windows\UsrClass.dat.LOG Object is locked skipped
C:\Documents and Settings\Administrator\Local Settings\History\History.IE5\index.dat Object is locked skipped
C:\Documents and Settings\Administrator\Local Settings\History\History.IE5\MSHist012006070120060 702\index.dat Object is locked skipped
C:\Documents and Settings\Administrator\Local Settings\Temp\Perflib_Perfdata_fa4.dat Object is locked skipped
C:\Documents and Settings\Administrator\Local Settings\Temp\~DF45AA.tmp Object is locked skipped
C:\Documents and Settings\Administrator\Local Settings\Temp\~DFC084.tmp Object is locked skipped
C:\Documents and Settings\Administrator\Local Settings\Temporary Internet Files\Content.IE5\index.dat Object is locked skipped
C:\Documents and Settings\Administrator\My Documents\GASTOS 2005 Y 2006\GASTOS MENSUALES JULIO 2006.xls Object is locked skipped
C:\Documents and Settings\Administrator\NTUSER.DAT Object is locked skipped
C:\Documents and Settings\Administrator\ntuser.dat.LOG Object is locked skipped
C:\Documents and Settings\LocalService\Cookies\index.dat Object is locked skipped
C:\Documents and Settings\LocalService\Local Settings\Application Data\Microsoft\Windows\UsrClass.dat Object is locked skipped
C:\Documents and Settings\LocalService\Local Settings\Application Data\Microsoft\Windows\UsrClass.dat.LOG Object is locked skipped
C:\Documents and Settings\LocalService\Local Settings\History\History.IE5\index.dat Object is locked skipped
C:\Documents and Settings\LocalService\Local Settings\Temporary Internet Files\Content.IE5\index.dat Object is locked skipped
C:\Documents and Settings\LocalService\NTUSER.DAT Object is locked skipped
C:\Documents and Settings\LocalService\ntuser.dat.LOG Object is locked skipped
C:\Documents and Settings\NetworkService\Local Settings\Application Data\Microsoft\Windows\UsrClass.dat Object is locked skipped
C:\Documents and Settings\NetworkService\Local Settings\Application Data\Microsoft\Windows\UsrClass.dat.LOG Object is locked skipped
C:\Documents and Settings\NetworkService\NTUSER.DAT Object is locked skipped
C:\Documents and Settings\NetworkService\ntuser.dat.LOG Object is locked skipped
C:\Program Files\ESET\cache\CACHE.NDB Object is locked skipped
C:\Program Files\ESET\logs\virlog.dat Object is locked skipped
C:\Program Files\ESET\logs\warnlog.dat Object is locked skipped
C:\Program Files\Microsoft Office\Office10\Macros\EUROTOOL.XLA Object is locked skipped
C:\System Volume Information\MountPointManagerRemoteDatabase Object is locked skipped
C:\WINDOWS\Debug\PASSWD.LOG Object is locked skipped
C:\WINDOWS\SchedLgU.Txt Object is locked skipped
C:\WINDOWS\SoftwareDistribution\ReportingEvents.lo g Object is locked skipped
C:\WINDOWS\Sti_Trace.log Object is locked skipped
C:\WINDOWS\system32\CatRoot2\edb.log Object is locked skipped
C:\WINDOWS\system32\CatRoot2\tmp.edb Object is locked skipped
C:\WINDOWS\system32\config\AppEvent.Evt Object is locked skipped
C:\WINDOWS\system32\config\default Object is locked skipped
C:\WINDOWS\system32\config\default.LOG Object is locked skipped
C:\WINDOWS\system32\config\SAM Object is locked skipped
C:\WINDOWS\system32\config\SAM.LOG Object is locked skipped
C:\WINDOWS\system32\config\SecEvent.Evt Object is locked skipped
C:\WINDOWS\system32\config\SECURITY Object is locked skipped
C:\WINDOWS\system32\config\SECURITY.LOG Object is locked skipped
C:\WINDOWS\system32\config\software Object is locked skipped
C:\WINDOWS\system32\config\software.LOG Object is locked skipped
C:\WINDOWS\system32\config\SysEvent.Evt Object is locked skipped
C:\WINDOWS\system32\config\system Object is locked skipped
C:\WINDOWS\system32\config\system.LOG Object is locked skipped
C:\WINDOWS\system32\h323log.txt Object is locked skipped
C:\WINDOWS\system32\wbem\Repository\FS\INDEX.BTR Object is locked skipped
C:\WINDOWS\system32\wbem\Repository\FS\INDEX.MAP Object is locked skipped
C:\WINDOWS\system32\wbem\Repository\FS\MAPPING.VER Object is locked skipped
C:\WINDOWS\system32\wbem\Repository\FS\MAPPING1.MA P Object is locked skipped
C:\WINDOWS\system32\wbem\Repository\FS\MAPPING2.MA P Object is locked skipped
C:\WINDOWS\system32\wbem\Repository\FS\OBJECTS.DAT A Object is locked skipped
C:\WINDOWS\system32\wbem\Repository\FS\OBJECTS.MAP Object is locked skipped
C:\WINDOWS\wiadebug.log Object is locked skipped
C:\WINDOWS\wiaservc.log Object is locked skipped
C:\WINDOWS\WindowsUpdate.log Object is locked skipped

Scan process completed.

REPORTE DEL EWIDO:
__________________________________________________
ewido anti-malware online scanner
http://www.ewido.net
__________________________________________________


Name: TrackingCookie.Atdmt
Path: C:\Documents and Settings\Administrator\Cookies\administrator@atdmt[1].txt
Risk: Medium

Name: TrackingCookie.2o7
Path: C:\Documents and Settings\Administrator\Cookies\administrator@micro softwga.112.2o7[1].txt
Risk: Medium


MUCHAS GRACIAS NUEVAMENTE POR SU AYUDA.