The only thing that the FX5200 has to "offer" over the the Radeon 9200 is its on-paper support of DX9. However, considering that the chip is very weak in graphics power, users won't even get to use the DX9 feature for decent framerates; in fact, a lot of game companies suggest that users should use DX8.1 and avoid the a game's DX9 option to make it actually playable. In effect, the DX9 feature set for the FX5200 is basically marketing. If you want a DX9 card that can be run fanless by default, the Sapphire Radeon 9600 Pro Ultimate is a good start.
Since you intend to use your system for media center capabilities, I would not certainly not reccomend using a high-end gamer card unless you intend to play HF2 or Doom3 (assuming they eventually come out
). I have the Sapphire Radeon 9200 and am completely satisfied with it -- it comes fanless, provides great image quality, and plays games such as Wolfenstein: Enemy Territory great at 1028x768 resolution 32-bit color (b/c its based on Q3 engine).
Either card from NVIDIA or ATI should be fine in your media center pc, however. If you want an integrated tv tuner with your video card, skip NVIDIA's yet-to-be-refined media center solution and go for the ATI All-In--Wonder series. I believe that the highest AIW card that comes fanless is the AIW 7500 (in which graphics power shouldn't matter since you only play movies and watch tv).
If you decide to go separate video card and tv tuner...
Unless you're a die-hard techno fanatic that must have the latest and greatest (one of my best friends is
)I wouldnt go for the HDTV tuner cards right now as they're rather pricey. A rather nice value is the Leadtek TV Tuner 2000 Deluxe that can be easily found for a good price at www.newegg.com