Hi.
I'm running a B5 campaign at the moment, and unlike some D20 conversions the B5 game works very well.
Aside from (as has been said) combat being appropriately deadly, the one thing I realised that I needed to keep in mind was a level of contitnuity with the show. Even the littlest scenario needs to feel like its in the B5 universe, which isn't as easy as it sounds.
Also, a lot depends on what era your game is going to be set in. For instance, my game runs parallel to the B5 series itself showing those events from a different perspective, but a game could easily be set during the Earth/Minbari war, the Dilgar war, the Telepath Crisis, the Drakh war or the "unknown" years of the ISA. Each time frame comes with its own feel.
Now this may just be my experience, but since the combat system is deadly, the game tends to revolve around skills rather than needing a level/CR system like D&D does. So, its possible to pick up different sci-fi modules (Traveller, Star Wars....etc) and with a little tweaking use them with little difficulty.
Mongoose have their own boards and the game gets a lot of friendly discussion, and its worth you dropping the same question there to get some more good advice. For reference, I post as Eryx over there.
Heres the link:
http://www.mongoosepublishing.com/phpBB2/index.php
Good luck with the campaign.
