More silly Raid questions

I want to set up a Raid 0 because I understand it to be faster.

I would use 2 Western Digital 80 GB Special edition drives.

Can I set these up so that I have 20 gigs to Windows and the rest to data storage (for reformatting purposes) or does it all need to be one big drive? Can I reformat without losing everything on both drives? Do I need to get another drive to put info on that I don't want lost when I reformat?

(I am not worried about the array crashing)

Yep, what you need is partitions. You can set partitions up that act like a whole new drive, thus making one partition stricly for the OS, and the other for data. You can use 3rd party software (I.E. Partition Majic Pro) or FDISk