Since you are on a windows xp machine I recommend wamp http://www.wampserver.com/en/ or xampp (both apache) for developing with silverstripe. Both of those are popular so SS is usually well tested on those platforms and they include all the mods which make out of the box setting up much more straight forward. Or try upgrading to IIS7.0 - runs alot more stable on that compared to 5.1.
I would upgrade to IIS7 but I can't find any way to upgrade. As far as I can see, IIS7 is only available on Windows Server 2008. And I think similar for IIS 6. So it looks like since MS have decided to not allow us to upgrade IIS on XP then I guess another, better web server is the goer. Probably a good idea in any case since I'm starting to need to do things that IIS on XP just can't do.