PFK had a pretty detailed article about them a while back, but I'm not sure if I've got that issue here at Uni. Garra are pretty easy to keep, the largest species reaches 4" but others are smaller. Like cooler water (but should be fine in general tropical temps as long as there's a decent oxygen content) and a bit of a flow.
I watched this fascinating tv programme about hippos ages ago which showed how their dung supported the whole ecosystem of the river. Several species of Garra lived around the hippos and fed off their dung, as well as 'cleaning' the hippos skin etc (the dody link was an article about how Garra can be used to help cure certain human skin conditions).
The Hippos rely on the Garra and other fishes to such an extent that they actually stand there with their mouths open to be cleaned and then they NEVER swallow any fish.
Unforunately, a decline in the number of hippos is screwing over the entire ecosystem...
Wicked fish, I might set up a special Garra tank when I get home.
Hope this helps, s'all I could really remember.
Cheers,
Luke.