How to change the windows xp boot up screen with my own wallpaper?
unless you're capable of decompiling *.exe files or you're a programmer it's just not going to happen without 3rd party software because the xp boot screen is hard coded into 'ntoskrnl.exe'.
if you mess around with that file and screw it up you've a fair chance of also screwing up windows and needing to reinstall.
one of many automatic boot screen changers can be found here:
http://www.topdrawerdownloads.com/downlo鈥?/a>
http://www.wincustomize.com/skins.aspx?l鈥?/a>