Nope, you cant switch between 32 bit and 64 bit without a clean install, which you should be doing anyway, it makes the system run a bit smoother and you avoid any potential issues. Also you probably want to skip vista and go straight to 7, its nicer than vista and runs a little smoother IMO.
Dont forget also you need a CPU that can run 64bit if you are on an older Pentium 4 system then you might have a problem going 64bit. Another issue you might find if its an older prebuilt system you could have problems finding drivers for 64bit OS.
You can use an upgrade version. You just can't upgrade the installed XP installation. However Vista does support upgrade from XP 32 to Vista 32. But like the other poster said, just do a clean install.
You can use an upgrade version. You just can't upgrade the installed XP installation. However Vista does support upgrade from XP 32 to Vista 32. But like the other poster said, just do a clean install.
you can upgrade xp to vista if both are 32bits. But you will never be able to upgrade an 32 bits OS to a 64 bits one without a clean installation