A/D converter speed doesn't care about oscillator speed, well, not really. The A/D converter will only run as fast as it will run, doesn't matter how fast you run the oscillator.
The older A/D converters will 'only' run at about 20ksps, the new ones around 100ksps. Problem is, once you get up to those speeds, you're going to need good filtering at the front end.
Thats the problem, I know that is kilo samples per second, but as far as filtering I am lost. I have never had to deal with this stuff before.

thanks.