REMOVING VISTA

I have stupidly installed Vista on my pc and now i want to re-install XP.

I have tried to do a clean install,(I must be doing something wrong.)
I have followed some advice and started using the Vista DVD to start the
process off the n change to the XP Disc this hasnt worked.

I have tried to run my Xp Disce and the Install icon is low-lighted.

I can get to page of Vista installation, where it shows whic hdrives to
select. ( ithought i could delete or edit from here)

I have followed microsoft help files and this hasnt worked.

Please help!