ok - confirmed on multiple computers - Vimeo embed code doesn't work on this site when viewed with IE7 (XP and 2k3 server). I can be viewed with Firefox. The problem seems to be that in IE the forum inserts some html tags that don't belong in the code.
If you insert the code with IE7, it absolutely doesn't work (see above post).
Inserted with Firefox it seems to work just fine - here an example
2-1 exhaust pipe KTM 950