Wow! A tower for 100$ either he is a very good friend or didnt know its value.
It can probably be sold for 5x more in less than a day! You are lucky!
I really whish I could get myself a G5 this year but unless I am able to trade / sell my PB, I will have to wait a year or two since I had the stupid idea to buy a loft and will know the joy of morgage...