I prefer black bars on the sides of the screen rather than stretching when playing a game that needs to run 4:3. The setting is rather buried. Perhaps some screen-shot ninja can come along and add screenshots for these settings windows.

Windows XP:

Right click on the Desktop to bring up the Display Properties.
Under the Settings tab, click the Advanced button to bring up the Chrome9 control panel.
On the S3 Display tab, uncheck the option “Expand Image Preferred.”

Now, when you launch a game that wants to resize the desktop it should create black bars rather than stretching for a much clearer picture.