If you use the Dragonstwar weapon damages, yes, it will be to lethal. (A Blaster will make what? 3d6?, approximately half of the hits will make your characters make massive damage threshold check)
If you want to make it as easy as possible, use the D20 Modern weapon damages for all weapons, with the following changes:
It is possible to buy laser and blaster equivalances for all standard weapons.
Blaster weapon deals the listed amount as electricity damage.
Laser weapons deal the listed amount as fire damage.
Optional changes:
Up Blaster damage by 1 size category (d6 becoming d8 and so on), increase price.
Up Laser Range by 50% (or another amount), increase price.
I think everything else can be kept the old way. If you do not want to have a headache, do not try to mix D20 Modern Classes with the D&D classes. Use only the set of one of the classes.
Dragonstar probably works best with D&D standard classes considering the typical monsters in Dragonstar. (It is D&D in Space, remember?)
You might consider using the follwing D20 Modern or Spycraft Rules in addition:
Action Dice. I think it is one of the best things of D20 Modern and Spycraft, it reminds me from Karma Dice in Shadowrun. It really helps everybody. (Don`t forget to give the NPCs them as well)
For making skill choices easier, consider using some of the D20 Modern skill sets, especially Knowledge (better defined this way), and recombine the skills as made their (now Use Rope or Innuendo Skill and so on)
Mustrum Ridcully