Can't figure out which is the trojan/hijacking program

I have a computer that has its home page hijacked by either malware or a trojan.  Here is the Hijaack this log:
Logfile of HijackThis v1.99.1
Scan saved at 6:05:36 PM, on 5/8/2006
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\spoolsv.exe
C:\PROGRA~1\Grisoft\AVG7\avgamsvr.exe
C:\PROGRA~1\Grisoft\AVG7\avgupsvc.exe
C:\PROGRA~1\Iomega\System32\AppServices.exe
C:\WINDOWS\System32\nvsvc32.exe
C:\WINDOWS\Explorer.EXE
C:\WINDOWS\system32\dcomcfg.exe
C:\Program Files\Logitech\iTouch\iTouch.exe
C:\PROGRA~1\Grisoft\AVG7\avgcc.exe
C:\PROGRA~1\Grisoft\AVG7\avgemc.exe
C:\Program Files\Common Files\InstallShield\UpdateService\issch.exe
C:\Program Files\TrustSoft AntiSpyware\TrustSoftAntiSpyware.exe
C:\WINDOWS\System32\NILaunch.exe
C:\Program Files\SpyKiller\spykiller.exe
C:\Program Files\Yahoo!\Messenger\ypager.exe
C:\WINDOWS\system32\RUNDLL32.EXE
C:\Program Files\Logitech\MouseWare\system\em_exec.exe
C:\Program Files\Logitech\iTouch\kbdtray.exe
C:\PROGRA~1\Grisoft\AVG7\avgw.exe
C:\WINDOWS\system32\msiexec.exe
C:\Program Files\Lavasoft\Ad-Aware SE Plus\Ad-Aware.exe
C:\PROGRA~1\WINZIP\winzip32.exe
C:\unzipped\hijackthis\HijackThis.exe

R1 - HKCU\Software\Microsoft\Internet Explorer,SearchURL = http://www.begin2search.com/sidesearch.html
R1 - HKLM\Software\Microsoft\Internet Explorer\Main,Search Bar = http://red.clientapps.yahoo.com/customize/ie/defaults/sb/ymsgr6/*http://www.yahoo.com/ext/search/search.html
R0 - HKLM\Software\Microsoft\Internet Explorer\Main,Start Page = http://red.clientapps.yahoo.com/customize/ie/defaults/stp/ymsgr6/*http://www.yahoo.com
R1 - HKCU\Software\Microsoft\Internet Explorer\Search,SearchAssistant = http://www.begin2search.com/sidesearch.html
R1 - HKCU\Software\Microsoft\Internet Explorer\SearchURL,(Default) = http://us.rd.yahoo.com/customize/ie/defaults/su/msgr7/*http://www.yahoo.com
R1 - HKCU\Software\Microsoft\Windows\CurrentVersion\Internet Settings,ProxyOverride = localhost
O2 - BHO: Nothing - {b0398eca-0bcd-4645-8261-5e9dc70248d0} - C:\WINDOWS\system32\hpB1A3.tmp
O3 - Toolbar: Yahoo! Toolbar - {EF99BD32-C1FB-11D2-892F-0090271D4F88} - C:\Program Files\Yahoo!\Companion\Installs\cpn1\yt.dll
O4 - HKLM\..\Run: [Logitech Utility] Logi_MwX.Exe
O4 - HKLM\..\Run: [zBrowser Launcher] C:\Program Files\Logitech\iTouch\iTouch.exe
O4 - HKLM\..\Run: [AVG7_CC] C:\PROGRA~1\Grisoft\AVG7\avgcc.exe /STARTUP
O4 - HKLM\..\Run: [AVG7_EMC] C:\PROGRA~1\Grisoft\AVG7\avgemc.exe
O4 - HKLM\..\Run: [AVG7_RegCleaner] C:\PROGRA~1\Grisoft\AVG7\avgregcl.exe /BOOT
O4 - HKLM\..\Run: [ISUSPM Startup] C:\PROGRA~1\COMMON~1\INSTAL~1\UPDATE~1\ISUSPM.exe -startup
O4 - HKLM\..\Run: [ISUSScheduler] "C:\Program Files\Common Files\InstallShield\UpdateService\issch.exe" -start
O4 - HKLM\..\Run: [TrustSoftAntiSpyware] C:\Program Files\TrustSoft AntiSpyware\TrustSoftAntiSpyware.exe /STARTUP
O4 - HKLM\..\Run: [NvCplDaemon] RUNDLL32.EXE C:\WINDOWS\System32\NvCpl.dll,NvStartup
O4 - HKLM\..\Run: [nwiz] nwiz.exe /install
O4 - HKLM\..\Run: [Net-It Launcher] C:\WINDOWS\System32\NILaunch.exe
O4 - HKCU\..\Run: [SpyKiller] C:\Program Files\SpyKiller\spykiller.exe /startup
O4 - HKCU\..\Run: [Yahoo! Pager] C:\Program Files\Yahoo!\Messenger\ypager.exe -quiet
O4 - HKCU\..\Run: [updateMgr] C:\Program Files\Adobe\Acrobat 7.0\Reader\AdobeUpdateManager.exe AcRdB7_0_5 -reboot 1
O4 - HKCU\..\Run: [NvMediaCenter] RUNDLL32.EXE C:\WINDOWS\System32\NVMCTRAY.DLL,NvTaskbarInit
O4 - Global Startup: Adobe Reader Speed Launch.lnk = C:\Program Files\Adobe\Acrobat 7.0\Reader\reader_sl.exe
O4 - Global Startup: Microsoft Office.lnk = C:\Program Files\Microsoft Office\Office\OSA9.EXE
O9 - Extra button: Messenger - {FB5F1910-F110-11d2-BB9E-00C04F795683} - C:\Program Files\Messenger\msmsgs.exe
O9 - Extra 'Tools' menuitem: Windows Messenger - {FB5F1910-F110-11d2-BB9E-00C04F795683} - C:\Program Files\Messenger\msmsgs.exe
O16 - DPF: {17492023-C23A-453E-A040-C7C580BBF700} (Windows Genuine Advantage Validation Tool) - http://go.microsoft.com/fwlink/?linkid=39204
O16 - DPF: {227F25BE-BCDC-11D0-BA80-0000F6181652} (CLRMachineInfoCtl Class) - http://eformrs.com/RSLoginModule.cab
O16 - DPF: {2BC66F54-93A8-11D3-BEB6-00105AA9B6AE} (Symantec AntiVirus scanner) - http://security.symantec.com/sscv6/SharedContent/vc/bin/AvSniff.cab
O16 - DPF: {644E432F-49D3-41A1-8DD5-E099162EEEC5} (Symantec RuFSI Utility Class) - http://security.symantec.com/sscv6/SharedContent/common/bin/cabsa.cab
O16 - DPF: {B9191F79-5613-4C76-AA2A-398534BB8999} (YAddBook Class) - http://us.dl1.yimg.com/download.yahoo.com/dl/installs/suite/yautocomplete.cab
O23 - Service: AVG7 Alert Manager Server (Avg7Alrt) - GRISOFT, s.r.o. - C:\PROGRA~1\Grisoft\AVG7\avgamsvr.exe
O23 - Service: AVG7 Update Service (Avg7UpdSvc) - GRISOFT, s.r.o. - C:\PROGRA~1\Grisoft\AVG7\avgupsvc.exe
O23 - Service: InstallDriver Table Manager (IDriverT) - Macrovision Corporation - C:\Program Files\Common Files\InstallShield\Driver\1050\Intel 32\IDriverT.exe
O23 - Service: Iomega App Services - Iomega Corporation - C:\PROGRA~1\Iomega\System32\AppServices.exe
O23 - Service: Macromedia Licensing Service - Unknown owner - C:\Program Files\Common Files\Macromedia Shared\Service\Macromedia Licensing.exe
O23 - Service: NVIDIA Display Driver Service (NVSvc) - NVIDIA Corporation - C:\WINDOWS\System32\nvsvc32.exe

I am running AVG virus software, and have scanned the computer with Ad Aware and Spykiller and Symantec's online virus scanner.  All say no problems. Yet when I open IE, it goes to a site selling security software and there is an icon in the system tray that ominously warns of the computer being infected with a virus.

Any help will be greatly appreciated!