when you have your tga's, import teh 1st one to VirtualDubMod or something similar, render the output as .avi and compress it with xvid. If you want to edit your vid, render as uncompressed .avi, import to vegas, edit and then render as xvid-compressed .avi
i guess you youse x264, if you put the quality 2 high with it... than the movie is getting slower... (is at my pc than) maybe you have to put your quality a bit down to like 80%
or just to the timescale up =)