How long a section do you wish to reverse? If it's not a whole lot, you could split your clip up frame by frame, then drag the frames into reverse order. Yeah, this would be very annoying for more than a few frames, but it could be done. The sound will probably be pretty weird though. You might want to render the sound out to a .wav file first, remove it from the timeline, reverse it in some other program, then import it back in.

This gets asked a lot. Here's the Sonic Foundry official answer (which is, get Vegas Video):

Sonic Foundry Answer

If you are reasonably techy, you can use VirtualDub. You save the AVI file as a series of BMP files, then use a file renaming program to number the files in reverse order. You then "Open" the series of BMP files (in VirtualDub) and then save the AVI file. You have to have a DV codec (like MainConcept) installed to recrease the AVI file.

If you don't have the MainConcept DV codec, you can skip the last step in the previous paragraph and instead import the BMP files directly onto the VideoFactory timeline, but you'll want to set the default length of a new BMP file to exactly one frame. You do this by holding the shift key while selecting VF's Preferences menu. Doing this gives you an extra tab in the Preferences dialog box called "Internal." Click on the "Internal" tab and then look around for "ntDefVideoStillLength." The default is 50,000,000 which is 5 seconds. You want 1/29.97002997 of that value which is 1,668,333. Remember to set it back when you're through. Also, it is best not to mess with any of the other values in this dialog box.