a bit embarrassing since i am a coder but i never asked the right questions about memory so i never understood and still dont understand the speeds etc.
im trying to rebuild this old machine with tight pockets
1. You should be able to use the ram, but if you can try to RMA it and trade for the correct DDR 400 ram. Otherwise you will throttle the capability of the motherboard. Newegg lists a 2x1 set of Corsair DDR 400 ram for $99.99, which would be slightly cheaper than the 4x512mb set that you now have. That would give you a 1T instead of 2T timing on the ram, it would cost less, and give you better performance than what you now have.
2. I don't think so. RMA the psu and get either a 24 pin or 20+4 pin psu. You didn't mention the brand or power of the psu, but I would suggest one from Antec, Enermax, Seasonic, or Thermaltake. Hyper also makes a good psu.