1 Vista HD(SATA)and 1 XP Home HD(IDE)

Okay, so here's my issue. I have 2 hard drives installed on my PC. 1 hard drive is a 140 GB SATA HD and has Vista Home Basic installed on it. The other is an 80 GB IDE HD and runs Windows XP Home, SP3. The XP home HD is the first one that was originally installed. I then installed the larger SATA HD and installed Vista Home Basic on it so I can learn Vista with all it's lovely glitches etc. At first all was great. I'd turn on the PC and I had my choice of which system I wanted to start. That stopped working not too long after. Just XP Home would boot. When I disconnect the XP HD and tried to boot to the Vista HD, it came up and said missing file. (Sorry, can't remember which file was missing). So, I reloaded Vista and it backed up my old files. But, the problem is this: When I turn on the PC, it goes straight to the XP Home system and doesn't show me both systems and which to choose from. I know it's probably something really stupid that I've overlooked, but I'm drawing a blank. I also have this configuration: a CD/RW and a DVD/RW set up as master and slave together on one IDE cable. The other IDE cable is set to Master for the XP Home HD, and then the SATA (Vista) HD is also set as master. Actually, there is no setting on this hd that I can see to change it, but it is in it's own SATA cable anyhow. Ideas? Thanks! :banghead