Vista removed, XP put on. Now my PC won't work!

Question

A FRIEND of mine suggested removing Vista on my PC and adding XP because I was having numerous problems with none of my old software / programs being compatible and also kept getting blue screens and black outs. I trusted him becasue he is crazy about computers and builds his own etc...
WHAT A FOOL I WAS!!!!!!!
Now I can't install anything and my broadband and media player won't work because (I've been told) the PC's components are compatible only with Vista so won't, therefore, recognise XP.My FRIEND now doesn't know what to do and apparently because of the way he got rid of Vista and installed XP (kill disc?!) I can't get Vista back on it.PLEASE HELP ME... Is there anything I can do?