Gah! This is really causing me hassle today. Suddenly without warning \'@\' (at symbol) and \'\"\' (double quote) are trading places on my keyboard but ONLY in Visual Studio
In XP if more than 1 keyboard input language is installed (ex: Dvorak and Qwerty) XP will flip flop randomly, particularly back to the OS's default language, and it mostly only happens when using a Microsoft application. And I'm 100% sure I'm not hitting Alt+Shift or any other key combination. This same problem will probably haunt you no matter what keyboard mappings or languages you have.
The only fix is to remove the secondary language and only add it when you need it. The other solution is to use Vista, which I notice no longer suffers from this bug (that's been in there since I started using Dvorak back in 2003 and not even XP SP3 fixed it either).