Here's how:

1.Create a new sequence, set the tempo to that of your song. Using step-editing, or whatever method suits the way you work, enter your drumloop into the song so it fills one bar, i.e. a single whole note.
2.Hit "play", you will hear your drumloop play, and it will be RETRIGGERED at the correct intervals - but since the Tempo is off, it will sounds totally silly...
3.Go into "Track/Sound", find the "semi tone shift". Play with it and adjust the pitch of your loop so the length becomes correct.
4.If necessary, go into "fine tune" to adjust the last little glitch
5.Dial in the effect "31 Pitch Detuner". Route the loop thru the effect.
6.Now apply an EQUAL AND OPPOSITE pitch-shift to the loop. Do this by going into the "edit insert effect", pick preset "Detune", set wet/dry mix to 100% wet, and set "Voice1 Semi" to the same number of semitones 3, but in the opposite direction. Same for "Voice1 Fine". Set "Voice1 Level" to "0.0dB" and "Voice2 Level" to "OFF"

Now you should hear your loop in the correct tempo, and at the correct pitch. Actually, you can change the key of the song by additional tweaking "Voice1 Semi" in the effect section if you feel like it. Adjust other parameters to taste. RESAMPLE. DONE!