If you enable AA then you should lower the resolution, that's the main point of AA, you can run a lower res and get better quality than just upping the res! 4xAA hardly blurs textures so doesn't really need Ani, it does however run very slowly, QxAA and Ani gives better results than 4xAA and looks the same as 4xAA & Ani but is a LOT faster! You only ever need the lowest Ani setting too!
A lot of people got duped in to thinking the 4200-64MB is faster, it is only faster if nobody ever o/c any of the 4200 cards. 4200 o/c is 99% dependent upon the ns RAM used. Read it off the second line on your RAM chips, it's the last 2 numbers, eg. AB123CD45-EF40 denotes 4.0ns RAM which will averagely reach 550mhz. 3.6ns or faster reaches 600mhz and all types of RAM can be found on 128MB 4200 just as easily as 64MB 4200. Don't be glum though, your 4200-64MB is faster than both GF3TI500 and full blown ATI Radeon8500, both of which were $300 6 months ago and the vast majority also came with 64MB. Unfortunately for you, Commanche4 is one of the current games which does breach 64MB with full details on, perhaps use medium detail settings or drop the res / eye candy a bit. However, I've never played it nor SOF myself.
Utils like Coolbits, RivaTuner and Geforce Tweak Utility are all worth checking out. With any settings you're choosing between quality and perf and generally each game is best with different settings. If performance is suspect then, after ensuring your CPU is up to providing the data, it's worth deinstalling drivers, perhaps running Detonator Destroyer and the reinstalling either the latest official non-beta drivers from nVidia or manu website, then install DX8.1, it won't hurt to get the latest drivers for all of your hw including mobo and BIOS. If your CPU is a little underpowered then it's best to apply AA & Ani as this will help to use up the spare GPU power. Regarding the settings, most of the time it is down to personal preference.