XP can see 4GB's of RAM, but doesn't work with it very well. Unless you have the 64bit version of XP or Server 2003 you shouldn't be using that much, simply.
Windows or any program will not use more ram than it requires, if ram is low the program might have low framerate issues or freezing. But if there are more ram than needed, There won't be any problem when working a program or a game on that computer.
If you would like to remove excessive ram, you can take one of the ram card out. or limit the ram usage by certain settings.
For extensive support please ask the person you've bought the card from or ask / call a person that you believe is knowlegable about this subject.
XP can see 4GB's of RAM, but doesn't work with it very well. Unless you have the 64bit version of XP or Server 2003 you shouldn't be using that much, simply.
If Windows doesn't know how to use that huge amount of ram properly it'll get weird and confused, this can lead to poor performance. 4gb is a ton, too, why do you need that much now?