Windows XP doesn't usually have drivers for the display card (GPU) or display. The same is true for most Windows about motherboard chipsets, WiFi and other computer parts.
I read your post twice and can't find where you finished the install with all the post Windows work.
Note: Edited for grammar.
Right, bit of a complicated one here. One computer, three hard drives. One has Vista on it, the other two have XP. I want to use one of the XP drives but both have got problems with the screen resolution. Both have just had XP reloaded on them and both are stuck on 640 x 480, the slider just won't move. Other than that they seem to be running perfectly. The Vista one isn't running well at all, very slow, limited internet connection, updates constantly trying but failing to update, printer won't install... But the screen resolution is perfect with full adjustability. Both XP drives were working in the computers I took them out of, and it seems too much of a coincidence that they should both have the same thing go wrong while dormant. The motherboard seems unlikely as the Vista one doesn't have the screen resolution problem. Frankly, I've run out of ideas. Here's hoping someone on here can give me a pointer or two.