how do i disable the boot partition in xp?

Here is my problem:

My first drive got a rootkit trojan that completely corrupted my win xp pro. Afraid that I would lose data from that drive, I installed a new SATA 1 TB drive, formatted it to be bootable and installed win xp pro. It wourks fine. When I re-connected the old drive, it always has priority over the new drive in terms of booting first and the corrupted version of win xp pro runs. I assumed that if I connected the sata data cable into a different slot, the old drive would not boot first. At least that how it seemed to work with the old IDE drives....

How do I disable the old drive's ability to boot, or at least make it so it does not boot first??