Bring in still image sequences using the "Still image sequence" checkbox in the Open dialog, NOT as a series of stills on the timeline. There, you can set the framerate.
///d@
Sorry, to be more clear: I have to export at 29.97, but I exported one animation at 24 fps. So I need to manually lengthen the duration of each frame when I import it so that my video will sync up to the audio correctly. I stretched my video out artificially to match, but I don't know exactly what that value is to tell the post-house...thanks, D
Well, then bring the 24 fps animation into Vegas as a still image sequence at 24 fps and render it out to 29.97. Vegas will do the correct frame rate converion for you. Make sure to set the media properties for the still image sequence properly, particularly the "field order" property (interlaced if the still are interlaced, "(none) progressive" if they are not [most likely the case at 24 fps]).
If the stills are not interlaced, Vegas will do 2:3 pulldown to render 29.97 interlaced (60i) video.
If the stills are interlaced (which I doubt they are), turn on the event's "resample" switch and Vegas will deinterlace to 48p, frame blend, and render 60i.