Here are the values for the AVGA resolutions (with doubled horizontal resolution)
How to use them:
1. Close powerstrip
2. Open the file powerstrip.ini
3. Add the following lines under the [Custom Resolutions] heading.
(If the heading doesn't exist, just create it at the end of the file)
4. Save the file and start powerstrip
5. Go to to the "Custom resolutions" window.
6. Select "user defined" resolutions.
7. Mark all resolutions in the window
8. Click "add resolution" and restart windows if necessary.
All resolutions should now be available. To test them:
mame gauntlet -resolution 672x240
To change the windows desktop to one of these resolutions use the right slider in powerstrip. (The resolution will not be available in Windows' display properties)
This procedure worked for me with both a Radeon9200SE and a GeForce2.