OK, here is the Teenagent cover:
http://img232.imageshack.us/img232/5814/teenagent.png I also studied Red_153D's covers and here are instructions for those who want to make similar (if not totally identical) covers with the template:
FONT: Couldn't find the exact same font, but I used Lucida Sans, which is a common font and close enough to the original to fool at least some people at first glance.
SCREENSHOTS: Simply copy-paste from GOG descriptions, nothing else needed (except for cropping, maybe). The lowest image border is about 144 pixels up from the bottom border of the template.
GAME TITLE (BACK): Position is about 15 pixels from the left border of the template and 35 pixels from the top. I found that RGB color 64,64,64 works pretty well here. Font size 24 pixels(!) is pretty good.
GAME DESCRIPTION: Position is about 15 pixels from the left border of the template and 72 pixels from the top. I found that RGB color 90,90,90 works pretty well here. Font size 14 pixels(!) is pretty good.
SYSTEM REQUIREMENTS: Position is about 15 pixels from the last line of the game description, and again 15 pixels from the left border of the template. I found that RGB color 123,123,123 works pretty well here. Font size 12 pixels(!) is pretty good.
GAME TITLE (SIDE): Position is about 15 pixels down from the GOG logo area. I found that RGB colors 90,90,90 (font border) and 241,241,241 (font body) work pretty well here. Font size 26 pixels(!) is pretty good.
At least I'm happy with the results, even if it's not perfect and only tries to imitate the original artist's style.
Hopefully these instructions are at least somewhat helpful to somebody out there, of course depending on software and all that, some changes may be needed if someone tries to recreate Red_153D's style.