Prima di tutto vi ringrazio da adesso perchè so' che con il vostro aiuto risolverò questo grave problema
Ecco il log di Hijackthis (di cui non sapevo nulla prima di leggere questo forum)

Logfile of HijackThis v1.99.1
Scan saved at 13.02.15, on 24/10/2006
Platform: Windows XP SP2 (WinNT 5.01.2600)
MSIE: Internet Explorer v6.00 SP2 (6.00.2900.2180)

Running processes:
C:\WINDOWS\System32\smss.exe
C:\WINDOWS\system32\winlogon.exe
C:\WINDOWS\system32\services.exe
C:\WINDOWS\system32\lsass.exe
C:\WINDOWS\system32\svchost.exe
C:\WINDOWS\System32\svchost.exe
C:\WINDOWS\system32\ZoneLabs\vsmon.exe
C:\WINDOWS\system32\spoolsv.exe
C:\WINDOWS\Explorer.EXE
C:\PROGRA~1\Grisoft\AVGFRE~1\avgamsvr.exe
C:\PROGRA~1\Grisoft\AVGFRE~1\avgupsvc.exe
C:\PROGRA~1\Grisoft\AVGFRE~1\avgemc.exe
C:\Programmi\Zone Labs\ZoneAlarm\zlclient.exe
C:\WINDOWS\SOUNDMAN.EXE
C:\Programmi\Java\jre1.5.0_06\bin\jusched.exe
C:\Programmi\Logitech\ImageStudio\LogiTray.exe
C:\PROGRA~1\Grisoft\AVGFRE~1\avgcc.exe
C:\WINDOWS\system32\inetsrv\inetinfo.exe
C:\WINDOWS\system32\ctfmon.exe
C:\WINDOWS\system32\nvsvc32.exe
C:\WINDOWS\system32\LVComS.exe
C:\Programmi\Spyware Doctor\sdhelp.exe
C:\WINDOWS\system32\svchost.exe
C:\WINDOWS\system32\wscntfy.exe
C:\WINDOWS\system32\svchost.exe
C:\Programmi\AdunanzA\eMule_AdnzA.exe
C:\PROGRA~1\SPYWAR~1\swdoctor.exe
C:\PROGRA~1\WINZIP\winzip32.exe
C:\Programmi\HijackThis.exe

R0 - HKCU\Software\Microsoft\Internet Explorer\Toolbar,LinksFolderName = Collegamenti
R3 - Default URLSearchHook is missing
O2 - BHO: Adobe PDF Reader Link Helper - {06849E9F-C8D7-4D59-B87D-784B7D6BE0B3} - C:\Programmi\Adobe\Acrobat 7.0\ActiveX\AcroIEHelper.dll
O2 - BHO: (no name) - {53707962-6F74-2D53-2644-206D7942484F} - C:\Programmi\Spybot - Search & Destroy\SDHelper.dll
O2 - BHO: PCTools Site Guard - {5C8B2A36-3DB1-42A4-A3CB-D426709BBFEB} - C:\PROGRA~1\SPYWAR~1\tools\iesdsg.dll
O2 - BHO: PCTools Browser Monitor - {B56A7D7D-6927-48C8-A975-17DF180C71AC} - C:\PROGRA~1\SPYWAR~1\tools\iesdpb.dll
O2 - BHO: Class - {C46D35DF-E757-5730-4704-E2D06C63205C} - C:\WINDOWS\rhkuy1.dll (file missing)
O4 - HKLM\..\Run: [Zone Labs Client] "C:\Programmi\Zone Labs\ZoneAlarm\zlclient.exe"
O4 - HKLM\..\Run: [NvCplDaemon] RUNDLL32.EXE C:\WINDOWS\system32\NvCpl.dll,NvStartup
O4 - HKLM\..\Run: [nwiz] nwiz.exe /install
O4 - HKLM\..\Run: [SoundMan] SOUNDMAN.EXE
O4 - HKLM\..\Run: [NvMediaCenter] RUNDLL32.EXE C:\WINDOWS\system32\NvMcTray.dll,NvTaskbarInit
O4 - HKLM\..\Run: [SunJavaUpdateSched] C:\Programmi\Java\jre1.5.0_06\bin\jusched.exe
O4 - HKLM\..\Run: [LogitechImageStudioTray] C:\Programmi\Logitech\ImageStudio\LogiTray.exe
O4 - HKLM\..\Run: [LogitechGalleryRepair] C:\Programmi\Logitech\ImageStudio\ISStart.exe
O4 - HKLM\..\Run: [AVG7_CC] C:\PROGRA~1\Grisoft\AVGFRE~1\avgcc.exe /STARTUP
O4 - HKCU\..\Run: [CTFMON.EXE] C:\WINDOWS\system32\ctfmon.exe
O4 - Global Startup: Avvio veloce di Adobe Reader.lnk = C:\Programmi\Adobe\Acrobat 7.0\Reader\reader_sl.exe
O8 - Extra context menu item: E&sporta in Microsoft Excel - res://C:\PROGRA~1\MICROS~1\OFFICE11\EXCEL.EXE/3000
O9 - Extra button: (no name) - {08B0E5C0-4FCB-11CF-AAA5-00401C608501} - C:\Programmi\Java\jre1.5.0_06\bin\npjpi150_06.dll
O9 - Extra 'Tools' menuitem: Sun Java Console - {08B0E5C0-4FCB-11CF-AAA5-00401C608501} - C:\Programmi\Java\jre1.5.0_06\bin\npjpi150_06.dll
O9 - Extra button: Spyware Doctor - {2D663D1A-8670-49D9-A1A5-4C56B4E14E84} - C:\PROGRA~1\SPYWAR~1\tools\iesdpb.dll
O9 - Extra button: Ricerche - {92780B25-18CC-41C8-B9BE-3C9C571A8263} - C:\PROGRA~1\MICROS~1\OFFICE11\REFIEBAR.DLL
O9 - Extra button: (no name) - {CD67F990-D8E9-11d2-98FE-00C0F0318AFE} - (no file)
O9 - Extra button: Messenger - {FB5F1910-F110-11d2-BB9E-00C04F795683} - C:\Programmi\Messenger\msmsgs.exe
O9 - Extra 'Tools' menuitem: Windows Messenger - {FB5F1910-F110-11d2-BB9E-00C04F795683} - C:\Programmi\Messenger\msmsgs.exe
O16 - DPF: {9A9307A0-7DA4-4DAF-B042-5009F29E09E1} (ActiveScan Installer Class) - http://acs.pandasoftware.com/actives...ree/asinst.cab
O16 - DPF: {9D190AE6-C81E-4039-8061-978EBAD10073} (F-Secure Online Scanner 3.0) - http://support.f-secure.com/ols/fscax.cab
O18 - Protocol: livecall - {828030A1-22C1-4009-854F-8E305202313F} - C:\PROGRA~1\MSNMES~1\MSGRAP~1.DLL
O18 - Protocol: msnim - {828030A1-22C1-4009-854F-8E305202313F} - C:\PROGRA~1\MSNMES~1\MSGRAP~1.DLL
O23 - Service: AVG7 Alert Manager Server (Avg7Alrt) - GRISOFT, s.r.o. - C:\PROGRA~1\Grisoft\AVGFRE~1\avgamsvr.exe
O23 - Service: AVG7 Update Service (Avg7UpdSvc) - GRISOFT, s.r.o. - C:\PROGRA~1\Grisoft\AVGFRE~1\avgupsvc.exe
O23 - Service: AVG E-mail Scanner (AVGEMS) - GRISOFT, s.r.o. - C:\PROGRA~1\Grisoft\AVGFRE~1\avgemc.exe
O23 - Service: NVIDIA Display Driver Service (NVSvc) - NVIDIA Corporation - C:\WINDOWS\system32\nvsvc32.exe
O23 - Service: PC Tools Spyware Doctor (SDhelper) - PC Tools Research Pty Ltd - C:\Programmi\Spyware Doctor\sdhelp.exe
O23 - Service: TrueVector Internet Monitor (vsmon) - Zone Labs, LLC - C:\WINDOWS\system32\ZoneLabs\vsmon.exe

Ciao Ciao