Adding a 10,000 hard drive

I am planning on getting a 160GB HD and in the future add a faster drive like a raptor. My question is, is it easy to add this as a primary drive? What would u have to do to the 160GB drive first before adding the other?

Make one drive mast and the other slave. Or if they're SATA, you don't have to do a thing. At least, I didn't when I connected my two Raptors...

so if i have windows installed on the slave I should be ok

You should have Windows installed on the Master HDD.