pourquoi would you want to make acid loops if you dont have acid?
the acid section of sound forge is the one section i never use, but from what i gather, you select the area you want to loop, copy it to a new window, edit the acid properties, all found in the 'special' menu, and save.
now if you're looking to loop more than one section of the sample, the 'shift selection left', or 'shift selection right' options will take the selected amount of area, and flip it left or right, thus making perfectly even loops...
you've probably already figured this out, but unfortunately that's all i can help you with.
-Rob