If thinking about the Dual 2.5 GHz look up "Apple PowerMac LCS" on google and see what comes up. A few people have complained on the cooling system leaking. Including myself. Some have made out pretty well with a like for like change to the latest MacPro, and some have been left with a big bill.
I was on the latter, no regrets when I first bought the machine, but when it crapped out, it would have been a $1800 fix.
Anyways do your research. Now is not the time to get a PM Dual 2.5. I loved mine before it died, and plan on repairing it when I can afford it. All it needs now is the processors. Not cheap but doable.