Get any DX10 or DX11 card. I don't know your needs or System specs.
Assuming you don't game, get an ATI HD4xxx card with 512MB of RAM.
FYI, if you like Video, also get the free software the K-Lite package and use the included MPC-HC player. Turning on DXVA for MPEG2, VC-1 and AVC will enable hardware video decoding to take the load off your CPU. You can monitor the effect by enabling or disabling this feature and using CTRL-ALT-DEL to monitor your CPU.
ATI is your best bet. If you were building a gaming system I'd say wait for NVidia's new cards.
No. The Radeon 9200 won't cause problems. However you should have at least 2GB of regular RAM (optimally 4GB) to run 64bit Windows 7. Make sure your CPU is 64bit if it is older.
If you need more help, be more specific. I hope your question is answered.