I have a bunch of old parts lying around, including 1 GB of DDR2-800, an Biostar MCP6P Motherboard, and an AMD Athlon 64 X2 3800+, and a Geforce 7600, a 120GB HD, an 8x DVD player, and a 500W PSU, and cheap atx case. I can throw a copy of fedora or ubuntu on the HDD.
I know the 7600 is not going to connect to the HDTV with HDMI to carry sound and video Is this, combined with something cheap (A 5450, 5550, GT220/240 or GTS 430) enough to run Netflix/Hulu/youtube at 1080p as a cheap Home theater PC?
right now the fact all the parts (except a HDPC-ready vid card) are free is the main consideration to setting this up as a HTPC of sorts (mostly for just internet streaming on the big tv). I'm mostly concerned the older CPU can't handle it.
Is the 3800+ enough for this kind of use (1080p output with the help of an HD-capable card) or will this just stutter?
Should be alright with the cards you've mentioned as long as DXVA is working properly. For pure CPU decoding it would probably depend on the codec being used. VC-1 and h.264 are more difficult and it may struggle if DXVA is not kicking in.
Here's a post from someone with a 3800+ that had some stutter issues and said CoreAVC cleared it all up, so there's also that route.
Linux uses some kind of GPU hardware acceleration... though I haven't dabbled in the penguin world in quite a while so I haven't explored it myself. I do remember that Nvidia had much better support than ATI video and the "DXVA" of the linux world is "XVMC"