8, though only 3 of them are in usable condition. The other 5 are old 98/xp machines, they still work though the hardware in all of them is crap.
Main computer computer is a HP Pavilion H8-1234, with a updated video card (GTX 650) and a 3 TB drive. Also pulled the 2 gb stick from it, so it's 8 gb now, though I've another 8 gb set that I'm thinking of adding to it.
Backup computer is a HP Pavilion P6532F, though everything except the mobo has been changed out. (To a Phenom II X4 965, GT 520, 8 gb ram, a Antec 380W psu, and the 1 tb drive replaced with a 500 gb drive since I needed the 1 tb for a external enclosure)
Last is a crap-machines, slim design, can't remember the model number. Switched out the hdd to go into my backup computer, and put in a 160 gb drive. It's on 7 right now, though I'm thinking of wiping it and using it as a XP machine.