Win7 OEM fresh install: Partitioning? Add'l int. (slow) HDs?

My budget box will have Windows 7 OEM (Home Premium 64-bit) and Lightroom
3 installed on it by this weekend, but I thought I would get your
advise on hard drive set-up/partitioning (if necessary) etc.

I have an internal 7200 rpm Samsung Spinpoint F3 1TB drive. I also
have a couple of older/slower internal HDs that I could make use of
(optionally). I think they are a 160GB and a 320GB ATA and PATA drive.

I also will be using LaCie Minimus 2 TB hard drives externally via USB
3.0. I plan to put all of my photos on one and use the other for
backup.

Windows is not my strong suit and this will be my first experience
with Windows 7. I'm mostly wondering how best to make use of the
internal HD(s) as far as partitioning goes or putting what where.
FWIW, I will be getting Photoshop CS5 in the future
also. Any words of wisdom would be appreciated.