Incoming!!!!!!!!!!!!!!
Hey Wicket:
You asked the Loaded Question...
many belligerent threads have come and gone regarding "sweetening" vs. "mastering", with lots of grave "Don't do it yourself" warnings from do-it-yourselfers.
Anyway, to answer your question...
You sound like you want a compressor (and/or a band limiter). It will help accomplish your main function of getting your mixes louder by lowering the level of the highest peaks in the sound wave while raising the overall level.
Your levels clip, but the disc is only "half as loud" as the pros? That's because there's two concepts to keep in mind-- volume and RMS. A clipping level is at top volume, but may not seem all that LOUD. RMS is sort of a measure of loudness (not technically, but reasonably close enough for now). A file that peaks at -6dB but has a RMS of -10dB will sound quite louder in general than a file peaking at -2dB but with an RMS of -18dB. Hopefully, with a compressor you will be able to increase the RMS of the file (while slightly turning down the volume so you won't have any clipping).
Actually, SOund Forge has both a compressor and a band limiter built in--Graphic Dynamics is the compressor and Multi-Band Dynamics is the band limiter (sort of a blend between a compressor and an EQ). **Check the help files** for details on using them, I'm no expert with them myself and they can be tricky. And listen closely--too much compression will sound loud, but lousy.
Just a bit too much compression will sound GREAT-- until a few weeks after your demo release....
Now whether other board denizens will grant you license to call it "mastering" is another story.