There are 26 "available" letters, so theoretically you can have up to 26 drives. However, 2 of those (A: and B
are reserved for floppies, and you have 2 optical drives, so that leaves you with 22 available letters, ergo you can have up to 22 hard drives (assuming the hardware supports that many
). You can basically add as many as you need.
I believe that all SATA cables are the same, so any should do, although I could be mistaking. SATA drives are backwards compatable, so a SATA150 drive will work with a SATAII port and vice versa. Both cost basically the same, so I would get a SATAII drive (because I like the best). You shouldn't need to do anything in the BIOS unless you disabled SATA previously.
You can install the OS on a SATA drive.
Edit: I have that drive and I like it, it is really nice.
After googling your mobo, it appears you have 2 SATA150 connectors, so you should be fine.
Any generic SATA cable like this