Also two other facts:
1) Damage is more er,....damaging in T20 vs. Dnd.
You take forever to heal from lifeblood damage and even a single hit can be enough to drop a higher level character, which leads to....
2) Death comes a'visiting far more often and stays past his welcome in Traveller when compared to DnD. No clerics with raise dead or heal.
Make sure that your players realize that T20 gaming is different in a basic way; ie, that it is far better to think and plan an encounter than it is to go into it "hacking and slashing".(yes, I know that is true for all gaming systems
) While DnD can be dangerous/deadly, it pales when compared to a normal t20 campaign. Explain before you start your campaign that healing lifeblood takes several weeks, so chronologically close encounters that do damage to PCs have a higher chance of causing PC death. Player who are use to running back to the cleric after taking some damage are in for a rude surprise. Give some concrete examples on what damage an ACR or gauss rifle does to a person (on auto) or to really drive it home, add a PGMP example!
Players not use to PC death need to rethink their strategy or game play.
...or you can always cube the healing rate of an autodoc!
Good Luck and post when you have your first run!