Being a fan of STAR TREK means you obsess over TREK things like Tribbles. Here's a link to a video that compares the original episode THE TROUBLE WITH TRIBBLES (1967) with the revisit to that episode -- one that effectively mixed the original cast with the DEEP SPACE 9 cast via computer effects titled TRIALS AND TRIBBLE-ATIONS (1996).
Non-fans, please excuse this entry.
(Photos; top: original scene of Kirk dressing down the shore leave party from TOS; bottom: a SFX scene inserting 2 of the STAR TREK DEEP SPACE NINE characters in the middle of the line-up.)
1/21/07 UPDATE: A couple more side-by-side comparisons: