Here are some links to our helpful instructions ;-)

All viewers by or based on Linden Lab viewers, including on 1.x, 2.x and 3.x code, are technically compatible with grids based on the OpenSim server code. However, the basic viewers provided by Linden Lab have no features to connect easily to non-Linden grids.

We suggest that you use one of the third-party viewers instead, which have extra features to make life much easier. OpenSim also keep a list of compatible viewers. If you have used Second Life™, you may have heard of Firestorm, but Singularity and Kokua are very popular too.