Is there any chance you have a "web-accelerator" program running, such as the one offered by
Google?
Have you tried another browser, for example FireFox instead of IE?
An anti-virus program could be re-writing URLs - try disabling web anti-virus if it's enabled.
I can't think of much else off-hand but let me know if you continue to have troubles. I unfortunately do not have access to a Vista box for hands-on testing.
Regards