finding the right computer for windows 7

I have just bought the missing manual windows 7. There is a question on p 25 about whether an AMD Turion 64 ML 34 processor at 1.80 ghtz with 512 mhtz of Ram is better than a core duo 2.0 ghtz eiyh 1 gig of Ram iwth radion xpress 200 m gragphic card. This is the answer I want! I do not have a computer at the moment and wanted to find out before I purchased a computer what would be best. The page goes on to explain how to access the capability of your computer to cope with the new system. Could someone tell me what is the minimum you would need of ram etc. Plus I looked in the book about the 32 and 64 bit versions and could not find alot about it. I want to be able to access Youtube and have read online that people on Internet Explorer have found it difficult to access youtube using the 64 bit version. I believe this has something to do with what adobe uses. At present I know that some computers offer 32 and 64 bit versions but this is really confusing me and I would like to know what version would be best.