To Sven Kistner: In MMD3 i cannot find the possibility to repeat one track only. It is possible to repeat all at once.
The 3 state repeat button (no repeat/repeat all/repeat track) was introduced with Winamp 5.03. MMD3 was written for Winamp 3, and never updated for Winamp 5.
eye_onus made an update for Winamp 5, wich contains several bugfixes.
So no, it's not possible to use that function in MMD3, until Sven Kistner will update his skin, to be honest, don't expect an update for MMD3.