okay here we go,goto windows/system32/dllcache(you might have to turn on the hidden folders option in the folders options dialog)search for your program you want to change,rename the extension(.bak or whatever),file protection will cough up a dialog,asking you to put in you winxp cd,just press cancel,then another box pops up asking if you want to keep the changes or whatever,just press yes.
then go to where your program is(i assume it's in the system32 folder),rename the extension like you did before,then put the program that you have in the folder you want,windows again hacks up a box asking you to throw in the xp cd,press cancel,then another box,press yes and there you go,thats all you have to do.and if you want to you can copy the program into the dllcache folder.
hope i helped you out(without confusing the heck out of you.)
squiggy