I think this answers your question...
http://windows.about.com/library/tips/bltip568.htm
Basically, run Regedit and navigate to HKEY_LOCAL_MACHINE\Software\Microsoft\Internet Explorer\AboutURLs
The value you're looking for (I think) is NavigationFailure. Whatever it is set to, change it to:
res://shdoclc.dll/navcancl.htm
and IE should go back to behaving normally.
EDIT: It just occurred to me that whatever hijacked you may have overwritten the DLL itself. If the registry value above is already correct, that's probably what happened. You could try Googling for "shdoclc.dll". You might be able to find a place to download a clean copy of the file. Just drop it into C:\Windows\System32\ (rename the existing one first). It may not work if there are multiple versions of this file floating around, but it's worth a shot.