Frank Saunders replied
First eliminate any scumware.
See
Dealing with Unwanted Spyware, Parasites, Toolbars and Search Engines
http://mvps.org/winhelp2002/unwanted.htm
Note that AdAware and SpyBot S & D will each catch some things the other
won't. Also, each need to be updated before every use, even when just
downloaded. There's also a lot more to do than just those two programs.
Now my two cents
CAUTION: Amateur hour fix follows here. YMMV significantly. I don't
know if this will help Aaron but it worked for me so far. I spent
days trying to figure out what the problem was and how to fix it.
I had the same problem with IE6 SP1 in XP Pro, even after running
current versions of SpyBot SD, CWShredder, Hijackthis and repairing
the [HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\URL]
registry key according to Sandi's suggestion at
http://www.mvps.org/inetexplorer/ .
Consistently before and after spyware fixes, Hijackthis found a
registry key "R3 - URLSearchHook: (no name) -
_{CFBFAE00-17A6-11D0-99CB-00C04FD64497} - (no file)" which I then
deleted with no adverse effect.
Then, in [HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\URL]
there was a key for [Default] (value not set) that I deleted.
In HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\URL\Prefixes]
there was another key for [Default] (value not set) that I deleted.
I did NOT change the default in
[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\URL\DefaultPrefix]
After a restart, the keys came back in the \URL and \Prefixes but the
http///?%20 problem was gone. Wrong addresses now lead to the MSN
Search page (slightly less annoying than the error page)
I hope this helps and any commentary or warnings from those who know
more from me might help others.