with that motherboard, all you have to do is close the L1 solder bridges on the tbird. It is really an awesome board for overclocking. Make sure you have a good heatsink/fan for the CPU. The 800 would be fine really, maybe the 850 would be good if it is only like 10 bucks more or something. The 800 probably won't get up to 1gig where the 900 probably will, but if you ask me, whats the diff between 900MHz and 1gig. Both are damn fast. As far as the power supply, I disagree with all the talk on this forum about power supply issues. It seems that everyone on here jumps to blaming problems on the supply. Unless you are running like 6 drives, a big GeForce2 card, and 4 fans, 250W should be fine. I have built 2 duron systems that run fine with 250W.
"Water-Cooled CPU Runner"
Yep, the 900 Tbird might overclock a little higher, but probably not much. Just get that fastest CPU you can budget for and overclock from there. I have a TBird 900 that will only go to 1066mhz, a Duron 700 will go to 945mhz, and my 1.2Ghz CPU will reach 1370mhz. As for POWER SUPPLYS, it can make a difference. When I recently got my 1.2Ghz CPU, I got a new Antec Performance Series Case with a 300W Antec power supply. I put the system together and fired it up. It ran fine at 1.2Ghz, but when I tried to overclock a little, it locked up, so I overclocked less and it still locked up. I swapped out the Antec 300W power supply for my Sparkle Power 300W, FPS300GT, unit and was immediately able to over clock to 1333mhz, and further to 1370mhz. upon looking on AMD's website for the recommended power supplies for a 1200mhz CPU, the Antec 300W was not listed, but my Sparkle Unit was. So what I am saying is that all parts are NOT created equal. If you have a high quality 250W unit, you could be just fine, or worse, it may not run very well at all creating lockups. If it is on AMD's list than you are safe, check it out.