I'm in a similar search - I have retired my old Dell Dimension 8200 (2.4 P4 cpu, 2 GB RAM, 160 & 250 GB drives, ATI 550 Pro tuner card) to PVR duty. It is working pretty well with BeyondTV 4.0 and an old Radeon 9550 card and a clean XP Pro install.
My question is: for $100 - $150, what AGP card would provide really noticeable performance increases over my old 9550 card? Or would the $ even really produce a difference I could see? I am recording at high-quality with MPEG 2, generally things look pretty decent, my input is just analog cable (comcast). I'm currently feeding an old but sweet Sony 27" via the s-video line.
Reviews at NewEgg highly praise the SAPPHIRE 100131L Radeon X800GTO 256MB 256-bit GDDR3 AGP 4X/8X . Many mention loud fan, some temp issues and some size issues. Wonder if this is an OK card and if it will fit my old Dell Dimension 8200 mobo/case? I'll shop around on this one.
My current production rig is a Velocity Micro w/ AMD 4400X2, 3 GB of Crucial, 10k SATA Raptor main drive and a 7800 GTS, with a 400 GB SATA data drive. I use it mostly for audio recording/editing and video editing driving 2 monitors. I'm not expecting to ever use the old Dell for anything but a PVR for the rest of it's life. It's holding up realy well and spending around $125.00 for a good AGP graphics card seems like a way to keep it out of the dump for a few more years. Plus if my VM every dies I can play BF2 on the x800 while I'm waiting for parts! Hard core builders will turn up their noses at Dell, but I've slowly tweaked the old girl into a useful machine.