if you're trying to use divx/xvid encoded files...I suggest abondoning all hope of it working right now. (re-encode your clips in virtualDubMod with a lossless codec like huffyuv or lagarith)
you may need to render your footage before you can view the clips...
at any rate, I'd suggest looking through
a helpful vegas guide and
EADFAG
and as a side note...this should probably be in software help (at least you didn't post this in audio help)