How much to raise with 1500 stacks?

[Beck]

I believe the general consensus in the Party structure is to raise 3BB?? But how big a raise should you put in on the first levels, with larger stacks? I play Pokerroom where starting blinds are 10/20 and stacks 1500, and at Bodog with 5/10 blinds and 1000 stacks.

I've started raising 5BB, but encounter this a lot:
Hero raise to 100 with, 2 callers. Flop is KQ9r. Hero bets pot, 1 caller. Turn 8. hero goes all in, villain calls and shows Q9s.
He's playing a marginal hand that in the long run is -EV, but when he do hit the flop, and I have a very good hand too, I just don't know how to avoid being eliminated?? t against someone with a good hand