newbie mining question - if electric wasnt a factor

[chugachoochoo]

Hi
So i am pretty good with tech but havent really gave bitcoin a thought until i came across an article on reddit today.
Mining for bitcoins seems very interesting and i think i have a basic understanding of the principals.
I basically have access to a few dozen crappier computers (quad cores, 2nd gen i5s a couple with dedicated graphics most without) i also do not pay for electric (as long as i dont push my luck too hard)
I was wondering if i can have some advice on what i should do with those pcs. Is it worth it with such low end gear? Can i use mining software while my users arent on the pc and disable it when my users are active?
Lets say i was starting fresh and didnt have much money to invest but did have that unlimited(ish) electric, what should i do\buy?
Sorry if i am being annoying with all these questions
Thanks for your input!!!!!

[Gator-hex]

Any computer will do just stick some cheap $90 Ati 5830's in it, download Bitcoin wallet, get a wallet address, join a mining pool, download GUIMIner, and they'll hash 300MH/s each if you overclock them right.