i like vegas as well and use it, and if you want to tune it up your machine a bit more, assuming that you have Xp 32 bit, check out this handy trick - one time microsoft did it right, applies if you have 3+gb of ram on a 32 bit machine, it will NOT use 100% of your ram but you get a nice boost and yes you see the difference.
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http://www.microsoft.com/whdc/system...AE/PAEmem.mspx
other than that for encoding HD video, im on a core2 quad Q9300 overclocked to 3.3ghz w/ 4gb of ram and it works good, it all depends how many filters you apply as well.. the more filters (i.e. sharpen etc etc), the slower it goes..