On the normalize popup, click on the drop down box and hit "normalize peaks" which ampifies the signal by the amount required to get the biggest peak to exactly 0db. That will create all your sounds at roughly the same level of volume though not loudness.

Also what sort of mix are you talking about? Fixing levels between tracks in a DJ mix? If thats the case you would be much better of thinking about transporting the mix into Ableton then using subtractive EQing to get the levels correct before normalizing it in sound forge before mp3's it up.

If you just think to highlight individual tracks with low volumes and hit normalize and have it fix it it won't work, there will be an appreciable difference in volume between the music at either side of the break, which is why subtractive EQing can come into it in something like Ableton which has slick controls to allow you some control.