Season 1 Credits -- full theme song
[youtube]
http://www.youtube.com/watch?v=oeQ2aHnM9sY&feature=related[/youtube]
Season 2 Credits -- full theme song
[youtube]http://www.youtube.com/watch?v=V6eLSVmXBEA[/youtube]
Season 3 Credits -- full theme song
[Youtube]http://www.youtube.com/watch?v=ECQ1lULq0Gc[/youtube]
Season 4 Credits -- full theme song
[youtube]http://www.youtube.com/watch?v=2_Tv5f3agDw&NR=1[/youtube]
Season 5 Credits -- full theme song
[youtube]http://www.youtube.com/watch?v=vK8vBzLn4l0&feature=related[/youtube]
Season 6 credits -- middle section of theme song removed
[youtube]http://www.youtube.com/watch?v=7AfhJLDFWaI&NR=1[/youtube]
Season 7 Credits -- middle section of theme song removed
[youtube]http://www.youtube.com/watch?v=d-5HC44GRbk&NR=1[/youtube]
Season 8 Credits -- opening and middle sections of theme song removed
[youtube]http://www.youtube.com/watch?v=4Rw9TE3j8Y4[/youtube]
In summary:
Seasons 1-5: full theme song
Seasons 6-7: middle section of theme song removed
Season 8: opening and middle sections of theme song removed
This is likely how the theme song appaears on the dvds, and how it appeared during the show's original run. If my memory serves me correctly, they shorten the credits on some of the seasons when they run the episodes in syndicated reruns.