hi,
i didnt see your HD tuner?
*operating system?
XP MCE(XP normal does not have Media centre,and i think XP is not sold new,or soon wont be) or Vista?i recommend Vista HP64 OEM.
your AMD will handle most operations, same as my first HTPC, now have tri core.quad cores under $200
ram is 2 gig to start(pair of 2*2 gig DDR2 cost me $120 3 months ago CORSAIR), 32 bit uses max 3 gig,i use vista 64 bit, have 4 gig, soon as i can afford 8 gig.
HDD 250 gig good start, i now have 3 HDD at 1 tera, not enough after olympics....and all my unwatched DVDs,HD TV recordings!(KNIGHTS TALE IS 10 GIG)
mobo the gigabyte HD720 series has 2 channel analogue out,and 256 meg shared DVI out and VGA ports. next step up has 5.1 digital out(optic fibre for normal stereo)
HOPE I HELPED A NOOB TODAY

)
edit:
case: i use a purpose built HTPC case, an 17 silver****(sh it forgot brand name), look on ebay or shops,mine has 6 HDD,4*80mm fans very quiet) rack and is size of my pioneer amp.
blue ray rom/dvd burner now under $200.or 50 bucks a decent dvd burner
lastly...i recommend WMC wireless keyboard,and remote,cost me 100 bucks.