Well all you really need is a cheap low end system and then throw a good card or two, such as a 7970 or 5970, and then you have sort of a budget miner. Mining bitcoins really doesn't require much CPU power or RAM, just a decent graphics card or two. Or you could wait until ASICS are easy to get, but that might be awhile...
the problem is that people say when the ASICS come out it will be way harder to mine bitcoin