Partitions and having OS on HD question

Ok, well my systems currently worthless until I reinstall everything. One small device caused me a lot of headache today and I won't bother with the story. Luckily it was only software related (not Windows for once).

I'm getting a third drive, a Seagate 7200.9 80GB SATA. This will house my OS and maybe some Image files of CD/DVD media.

Questions.

1. How should I partition it so that I have enough room of XP SP2 with all updates and also have enough room for Vista (without having to partition it again). I'm thinking 40GB would be enough for Vista and whatever updates it needs for the next few years after its out.

2. Does partition a drive slow it down even if you're not multitasking on the drive (i.e., you're not doing something that requires all the partitions on the HD).

3. After I reinstall the OS, I'd like to copy my WinXP disc to my HD by creating an image file with Alcohol 120. With three HDs, if I set my BIOS to boot from my HDs, will it be able to figure out which one has the OS files in case I need them again in the future?