If you're using Microsoft's Virtual PC, you can download free releases of Windows XP SP3 that are intended for testing various versions of Internet Explorer at Microsoft Download Center. For your use, they should do nicely, though I do recommend evaluating the disk space requirements to determine if they're worth it.
If you want to use one of them with VirtualBox instead, here is the command to convert the VHD file (MS Virtual PC) to a VDI file (VirtualBox), assuming that the VirtualBox install directory is in your PATH at least temporarily and assuming that VirtualBox won't let you simply use the VHD file already (you might grab a beverage while you wait for the conversion to finish...maybe catch up on some sports or something; it took nearly ten minutes to finish on my machine, and the first part is just creating the file where it appears to always be at 0% while later it starts to actually write the data which apparently is a much faster process):
vboxmanage -q clonehd <full path to source VHD file> <full path to destination VDI file> --format VDI
There has been some talk of the compact feature not working in some 2.x versions, but that seems to be fixed in the release I'm using (3.1.2). I didn't see any difference after compacting, but for future reference, here is the command:
vboxmanage -q modifyvdi <full path to VDI file> compact
Note that the -q flag (the equivalent long option is --nologo) suppresses the header that is output to the screen containing the (long) program title, copyright information, etc. :P
VirtualBox Forums http://forums.virtualbox.org/viewtopic.php?t=687
Microsoft Download Center http://www.microsoft.com/downloads/details.aspx?FamilyId=21EABB90-958F-4B64-B5F1-73D0A413C8EF&displaylang=en