You will find more than enough info on these machines at xlr8yourmac.com. I have upgraded five or these babys in the last year and I have a few pointers to keep you out of trouble. First, if you have a rev 1 b&w and you want to add a bigger harddrive, you will need to get a pci controller that is compatable. You can also put a pci wireless card in for airport, but some people had success with the Lynksys and I did not. The Lynksys cards I got didn't work with b&w's or beige g3s. The very same model that many got to work. I ended up getting the buffalo card and antenna setup. Check out OWC or Newegg.com for these. The odd thing is that the Lynksys worked perfectly in my MDD dual g4 out of the box for 802.11g use with airport extreme. Go figure. If you are planning on running osx on a b&w I would strongly suggest you ditch your existing ram and get new sticks from Crucial. This is the only brand of ram I have found that consistantly works in the b&ws. I had all kinds of problems with old original apple ram and 3rd party ram when upgrading to osx. Trial and error and wasted money led me to the Crucial solution. If you are going to run os9, then don't worry too much about this topic. Some of the rev 1 machines will have bad onboard firewire ports. Again, a pci card will solve this problem, and they are relatively cheap. Lastly, if you want to add a faster processor,
I have to agree with bousozoku on this one. Go for the 800 or 900 g3 and it will be plenty zippy for 95% of normal computing. If you require a g4, then got one of those.