I've just released the 3G S version of my previous iPhone 4-only camera hack (see http://www.iphonelife.com/blog/87/how-you-can-make-your-iphone-4-much-more-versatile-video-camera ; please check out the iPhone 4 manual for more info on how the GUI works. The 3G S version is only a bit different from the iPhone4 one, so, your learning curve won't be so steep as when starting from scratch.).
The tool allows for greatly increasing resolution and fine-tuning data rate (in Simple view) and fine-tune all parameters (in Advanced view).
As usual, I also provide you with all the sources; see http://dl.dropbox.com/u/13100693/html/062011iPhone3GSCameraHack/iP43GSCamEnhancer.zip
The directly deployable Cydia package is on the same Cydia repo (http://www.winmobiletech.com/cy or http://winmobiletech.com/cy ). Make sure you download the 3GS-specific one and not the one for the 4.0! (See image below)
I've directly tested this on my 4.2.1 3G S. I couldn't directly test it on a 4.3+ 3G S. However, exactly the same codebase works just fine on the iPhone 4 4.3.x (where, in general, the only difference is a directory name) with different parameters; therefore, the utility should work on the 3G S 4.3.x too.
Feedback, bug reports etc. are welcome - and don't forget I'll post a full article, full of test videos and pictures, on what the different parameters do, in 1-2 days! (I just didn't want to wait any more with releasing the app itself before publishing the article. After all, you can use the app even without reading the article.)