All clear!
The problem was highlighted when I ran HijackThis, and several spyware entries were found. Deleting any old files can cause damage though so I checked with a security message board and they gave me instructions. There was also a dll in the C:WindowsSystem32 directory called SWin32.dll that I think was related to it, and that file was deleted.
Here's the HijackThis log if you want to see (now removed processes shown in red, ignore the yellow text, they're links):
Logfile of HijackThis v1.97.7
Scan saved at 17:21:00, on 23/06/2004
Platform: Windows XP (WinNT 5.01.2600)
MSIE: Internet Explorer v6.00 (6.00.2600.0000)
Running processes:
C:WINDOWSSystem32smss.exe
C:WINDOWSSYSTEM32winlogon.exe
C:WINDOWSsystem32services.exe
C:WINDOWSsystem32lsass.exe
C:WINDOWSsystem32svchost.exe
C:WINDOWSSystem32svchost.exe
C:WINDOWSExplorer.EXE
C:WINDOWSsystem32spoolsv.exe
D:AVGavgcc32.exe
C:WINDOWSSystem32ctfmon.exe
C:Program FilesUnited DevicesUD.exe
D:Intense Language OfficeCommonOffMan.exe
C:Program FilesUnited Devicesud_7174683.exe
D:AVGavgserv.exe
C:WINDOWSSystem32CTSvcCDA.exe
C:Program FilesUnited Devicesud_7174683_0.dirud_ligfit_Release.exe
C:WINDOWSSystem32HummingbirdConnectivity7.00Inetdinetd32.exe
C:WINDOWSSystem32HummingbirdConnectivity7.00JconfigjconfigdNT.exe
C:WINDOWSSystem32HummingbirdConnectivity7.00Jconfighjavaw.exe
C:WINDOWSSystem32nvsvc32.exe
C:Program FilesJavaSoftJRE1.3.1binjavaw.exe
C:WINDOWSSystem32svchost.exe
C:WINDOWSSystem32Tablet.exe
D:HijackThisHijackThis.exe
R0 - HKCUSoftwareMicrosoftInternet ExplorerMain,Start Page = http://news.bbc.co.uk/
R0 - HKLMSoftwareMicrosoftInternet ExplorerSearch,SearchAssistant =
R1 - HKCUSoftwareMicrosoftWindowsCurrentVersionInternet Settings,ProxyServer = hermes:3128
R0 - HKLMSoftwareMicrosoftInternet ExplorerMain,Local Page = C:WINDOWSSYSTEMblank.htm
R1 - HKLMSoftwareMicrosoftInternet ExplorerMain,SearchAssistant = about:blank
O2 - BHO: (no name) - {06849E9F-C8D7-4D59-B87D-784B7D6BE0B3} - D:PROGRAM FILESADOBEACROBAT 5.0READERACTIVEXACROIEHELPER.OCX
O2 - BHO: (no name) - {53707962-6F74-2D53-2644-206D7942484F} - D:SpyBotSDHelper.dll
O2 - BHO: (no name) - {5FA6752A-C4A0-4222-88C2-928AE5AB4966} - C:WINDOWSSystem32SWin32.dll
O3 - Toolbar: &Radio - {8E718888-423F-11D2-876E-00A0C9082467} - C:WINDOWSSystem32msdxm.ocx
O4 - HKLM..Run: [SystemTray] SysTray.Exe
O4 - HKLM..Run: [NvCplDaemon] RUNDLL32.EXE NvQTwk,NvCplDaemon initialize
O4 - HKLM..Run: [WheelMouse] C:WHEELM~1wh_exec.exe
O4 - HKLM..Run: [Intense Registry Service] IntEdReg.exe /CHECK
O4 - HKLM..Run: [QuickTime Task] "D:QuickTimeqttask.exe" -atboottime
O4 - HKLM..Run: [KernelFaultCheck] %systemroot%system32dumprep 0 -k
O4 - HKLM..Run: [AVG_CC] D:AVGavgcc32.exe /STARTUP
O4 - HKLM..Run: [Adstartup] C:WINDOWSSystem32automove.exe
O4 - HKCU..Run: [CTFMON.EXE] C:WINDOWSSystem32ctfmon.exe
O4 - HKCU..Run: [ILO_Office_Manager] IntEdReg.exe /OFFMAN
O4 - Global Startup: UD Agent.lnk = C:Program FilesUnited DevicesUD.exe
O8 - Extra context menu item: Download with GetRight - D:GetrightGRdownload.htm
O8 - Extra context menu item: Open with GetRight Browser - D:GetrightGRbrowse.htm
O9 - Extra button: Yahoo! Messenger (HKLM)
O9 - Extra 'Tools' menuitem: Yahoo! Messenger (HKLM)
O9 - Extra button: Messenger (HKLM)
O9 - Extra 'Tools' menuitem: Windows Messenger (HKLM)
O12 - Plugin for .spop: C:PROGRA~1INTERN~1PluginsNPDocBox.dll