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:\Windows\System32 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:\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\Explorer.EXE
C:\WINDOWS\system32\spoolsv.exe
D:\AVG\avgcc32.exe
C:\WINDOWS\System32\ctfmon.exe
C:\Program Files\United Devices\UD.exe
D:\Intense Language Office\Common\OffMan.exe
C:\Program Files\United Devices\ud_7174683.exe
D:\AVG\avgserv.exe
C:\WINDOWS\System32\CTSvcCDA.exe
C:\Program Files\United Devices\ud_7174683_0.dir\ud_ligfit_Release.exe
C:\WINDOWS\System32\Hummingbird\Connectivity\7.00\Inetd\inetd32.exe
C:\WINDOWS\System32\Hummingbird\Connectivity\7.00\Jconfig\jconfigdNT.exe
C:\WINDOWS\System32\Hummingbird\Connectivity\7.00\Jconfig\hjavaw.exe
C:\WINDOWS\System32\nvsvc32.exe
C:\Program Files\JavaSoft\JRE\1.3.1\bin\javaw.exe
C:\WINDOWS\System32\svchost.exe
C:\WINDOWS\System32\Tablet.exe
D:\HijackThis\HijackThis.exe
R0 - HKCU\Software\Microsoft\Internet Explorer\Main,Start Page = http://news.bbc.co.uk/
[color=red]R0 - HKLM\Software\Microsoft\Internet Explorer\Search,SearchAssistant =
[/color]R1 - HKCU\Software\Microsoft\Windows\CurrentVersion\Internet Settings,ProxyServer = hermes:3128
R0 - HKLM\Software\Microsoft\Internet Explorer\Main,Local Page = C:\WINDOWS\SYSTEM\blank.htm
R1 - HKLM\Software\Microsoft\Internet Explorer\Main,SearchAssistant = about:blank
O2 - BHO: (no name) - {06849E9F-C8D7-4D59-B87D-784B7D6BE0B3} - D:\PROGRAM FILES\ADOBE\ACROBAT 5.0\READER\ACTIVEX\ACROIEHELPER.OCX
O2 - BHO: (no name) - {53707962-6F74-2D53-2644-206D7942484F} - D:\SpyBot\SDHelper.dll
[color=red]O2 - BHO: (no name) - {5FA6752A-C4A0-4222-88C2-928AE5AB4966} - C:\WINDOWS\System32\SWin32.dll
[/color]O3 - Toolbar: &Radio - {8E718888-423F-11D2-876E-00A0C9082467} - C:\WINDOWS\System32\msdxm.ocx
O4 - HKLM\..\Run: [SystemTray] SysTray.Exe
O4 - HKLM\..\Run: [NvCplDaemon] RUNDLL32.EXE NvQTwk,NvCplDaemon initialize
O4 - HKLM\..\Run: [WheelMouse] C:\WHEELM~1\wh_exec.exe
O4 - HKLM\..\Run: [Intense Registry Service] IntEdReg.exe /CHECK
O4 - HKLM\..\Run: [QuickTime Task] "D:\QuickTime\qttask.exe" -atboottime
O4 - HKLM\..\Run: [KernelFaultCheck] %systemroot%\system32\dumprep 0 -k
O4 - HKLM\..\Run: [AVG_CC] D:\AVG\avgcc32.exe /STARTUP
[color=red]O4 - HKLM\..\Run: [Adstartup] C:\WINDOWS\System32\automove.exe
[/color]O4 - HKCU\..\Run: [CTFMON.EXE] C:\WINDOWS\System32\ctfmon.exe
O4 - HKCU\..\Run: [ILO_Office_Manager] IntEdReg.exe /OFFMAN
O4 - Global Startup: UD Agent.lnk = C:\Program Files\United Devices\UD.exe
O8 - Extra context menu item: Download with GetRight - D:\Getright\GRdownload.htm
O8 - Extra context menu item: Open with GetRight Browser - D:\Getright\GRbrowse.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~1\INTERN~1\Plugins\NPDocBox.dll
O16 - DPF: {11260943-421B-11D0-8EAC-0000C07D88CF} (iPIX ActiveX Control) - http://www.ipix.com/viewers/ipixx.cab
O16 - DPF: {166B1BCA-3F9C-11CF-8075-444553540000} (Shockwave ActiveX Control) - http://download.macromedia.com/pub/shockwave/cabs/director/sw.cab
O16 - DPF: {41F17733-B041-4099-A042-B518BB6A408C} - http://a1540.g.akamai.net/7/1540/52/20030530/qtinstall.info.apple.com/bonnie/us/win/QuickTimeInstaller.exe
O16 - DPF: {A8F2B9BD-A6A0-486A-9744-18920D898429} (ScorchPlugin Class) - http://www.sibelius.com/download/software/win/ActiveXPlugin.cab
O16 - DPF: {D27CDB6E-AE6D-11CF-96B8-444553540000} (Shockwave Flash Object) - http://download.macromedia.com/pub/shockwave/cabs/flash/swflash.cab
O16 - DPF: {DF780F87-FF2B-4DF8-92D0-73DB16A1543A} (PopCapLoader Object) - http://anu.popcap.com/games/popcaploader_v5.cab
O16 - DPF: {EF791A6B-FC12-4C68-99EF-FB9E207A39E6} (McFreeScan Class) - http://download.mcafee.com/molbin/iss-loc/vso/en-us/tools/mcfscan/2,0,0,4367/mcfscan.cab
O17 - HKLM\System\CCS\Services\Tcpip\..\{E156C0D7-EC1D-4C75-860F-24066892535B}: Domain = btinternet.com