I'd turn on 16xAF permanently. Try Performance first, and see if the IQ is good. If you notice distinct transitions between MIP-maps and it annoys you, move up to Quality. Then add AA as you see fit. Keep in mind the 9500P is really meant for AA+AF at 1024x768 max in newer games, as it doesn't have sufficient memory bandwidth to power higher resolutions with those features. Older games, you may get away with AA+AF at higher res than 10x7.
If you want to know exactly what your framerate is, download FRAPS 1.9 and use it. I say 1.9 rather than 2.0 b/c I've heard that ATi cards may have certain performance issues with 2.0, though I don't notice any issues with my Radeon 9100 and FRAPS 2.0 (and I really like the benchmark feature in 2.0).