Get this processor:
Athlon 64 3400+ 754
and you get a motherboard free with it as a combo deal.
mobo + proc = 100$ (proc is oem so you need a hsf for it)
hsf = about 20$
512mb ram = 50$
a decent psu at least 400w = about 30$ (one that comes with a case should be adequate)
Radeon 9600pro Red or blue = 60$
80GB sata hard drive = 50$
DVD burner = 30$
Decent case = 50$
Total = 400$
:
The fun of putting it all together = priceless
Whats in your wallet?
j/k
I have an athlon xp 2700+ with 512MB ram radeon 9600 and was able to do hd perfectly no stutter at all, that was with the HDTV wonder on pretty high bitrate atsc 1080i and 720p streams, and also those sample wmv|hd videos in 720p and 1080p were perfect.
So an a64 3400+ with a 9600pro would be even more capable.
Stop waiting and get a good system NOW and enjoy perfect hd and 4:2:2 without stutter.
If you already have stuff like that you could pull out of your old system you could save even more money.
Say you already have ddr ram lying around or in your old computer you can take the ram out of the list, a case and psu, your old hard drive and cd drive.
Now your down to just 180$
The only thing I did not include was the os which is about 100$ for xp home.