Fallout 3 expansions questions?

ok i know this is probly a stupid question but im just making sure for my money's sake

currently i only have 800 points and im going to buy Broken steel for fallout 3, but i dont have the other expansions. if i go and buy the other ones at a later time i will still be able to access them and use them to reach level 30 correct?

i know its probly a yes but im just making sure

Yeah you can buy them in any order...

ok good thats what i thought. going to my 360 to purchase now :D

ok broken steel question here: wheres the tri-beam laser rifle?

you can find the tri-beam laser rifle on super mutant overlords

umm second broken steel question: where can i find a super mutant overlord?

when u r over level 20 they will spawn in the place of other super mutants around the wasteland.