Also, check out Andy Slacks Halfway Station website for a GURPS-lite driven sourcebook for "SG-13", which is rather good.
I have yet to here anything definintive about official games for either B5 (beyond JMS cryptic comment) or SG-1, although Matt Sprange of Mongoose was intriguingly elliptical in a thread at EN World.
I think a lot of the OGC from T20 would work very well for d20 versions of both (my own half completed B5 game is a variant of CT/MT/T4), particularly the prior history and psionics stuff for B5. But I'm not aware of anyything "official"