Scanning high res on Mountain Lion?

Scanning in high resolution may not get you the results you expect and may be overkill for the final result depending what you do with the scan; i.e. print, display, etc. In as much as the Epson Stylus SX200 is not directly supported on the Mac via Epson Scan program try a third party program like VueScan.

High res scan will not make a very small image better when enlarged. You are dependent upon your original and your output.

It's a good scanning program with lots of features.

How good of a result you can get from a small original depends very much on the optical quality of your scanner, its Dmax, and the software being used.

Optics quality isn't just the scanner's touted DPI. It's also the quality of the lens system itself. You could have a scanner with a high DPI step rating, but still get lousy scans if it has a cheap lens.

Your model has a scanning DPI of 1200 (ignore the larger number), which is okay. No idea what Dmax it is, can't find any information that mentions it. But considering its price, I can't imagine it's any higher than 3.0, if it's even more than 3. This is at least, if not more important than resolution. Especially if it's a slide, or other small transparency you're trying to scan. The density of slides is much higher than reflective items, and so requires a higher Dmax to capture any type of highlight and shadow detail.

Given the model, you just aren't going to be able to get as good a scan as you would like from a small original. It's physically incapable of doing so. Reflective or transparent.