How does one go about useing loops THAT WORK SEMELESSLY WITH GB
The best solution for additional GarageBand loops would be to get the JamPacks, i.e. JamPack "Remix Tools" and "Rhythm Section". These will give you plenty of drum beats and grooves.
The Jam Packs have been discontinued, but you get them all, when you buy Mainstage 2 at the AppStore for a moderate fee. Mainstage 2 will install all Jam Packs and additional instruments in the same place where GarageBand and Logic loops and instruments are installed, so you can use them seemlessly from GarageBand as well. And the price for MainStage 2 with all JamPacks included is as far less than the price for a single JamPack used to be.
Alternately search the Bullets & Bones FAQ for free loops http://www.bulletsandbones.com/GB/PlugInsDrumLoops.html