Just to update you on how this is going.
Got the new hard drive through, it took me 2 hours to get the BIOS to see the drive despite me trying just about everything. Eventually I got it to work by hot plugging it while windows xp was active and resetting machine. The xp drive is IDE master plugged into SATA2 and the new drive is IDE slave plugged into SATA4.
Next problem, it took me a further hour to figure out how to change the boot order in the BIOS. The normal boot order menu did not contain the new drive, however there was a separate option menu to change the order that the hard drive's booted, once you changed that then the boot order in the 'main' boot menu (if I can call it that) then gave the new drive. After all that I was exhausted, and decided to leave it for now, will try to continue this process in another few days. I hope u now see why I wanted to keep my XP drive installed.
Speaking of boot order, to install win7, I put the disc into the dvd drive (obviously). Is my proposed boot order correct?
1) DVD drive
2) New un-inititated drive (for win7)
I say this because I presume that when win7 is installing it will reset itself a few times and it is important that it boots into the win7 new drive.