Vista/XP Dual boot... again :)


Hi guys, new to the forums. Recently I got a new rig with 2x320GB SATA hard drives. On one, Vista Home Premium came preinstalled. On the other, I've been trying to install XP, but unawares I've been using an OEM disk (stupid stupid stupid) instead of the normal version I have lying around somewhere. Now, what I want to do is install XP on the second disc and keep Vista on this one. So far, the closest I've managed to a dual boot is one that presents a screen with three options to start XP, each of which... you guessed it, start XP. Very frustrating.
I would really really appreciate it if someone could write me a printable guide which will allow me to install XP on the other hard drive and successfully add the dual boot screen from XP (which I'll have to do seeing as XP wipes the boot options). My life would be alot simpler if I could just wipe everything, install XP then install Vista, but unfortunately its not an option, as I've already lost valuable work from the first reinstall of Vista. Plus, my ISP has already called with irrate demands as to why I've downloaded so much lately (had to re-download ALOT of drivers and packages).
So, could anyone please help?