Well, I've actually had this problem in my group as well. I play online(via yahoo messenger and conferences) and offline. My online group is painful, but my tabletop game is less so, though I do have two players who are powergamers. Let me breakdown the group for you. I have myself (I also play a NPC just because its more fun for me and because it allows the PC's more options when making their characters. Having 4 characters means that its a game of "not it" for playing the bandaid. This allows people to choose what they want to play and I get to make something to fill the slot. Currently we have a rogue, a wizard, a sorcerer, a ranger, and myself as a battlecleric (cleric focused on fighting, not separate class)). One player I have gamed with since my first days in D&D. The first half year he played a cleric every character until somebody forced him to play something different, since then he has been a huge roleplayer), we have two guys who have been playing for about a year now in a different group, and then we have our last player who is there just because she is a friend. She really is mostly a fifth wheel and she prefers it that way. She makes a character to feel like she has something to do with the game and just watches. Nobody is harmed by it so I don't do much more than encourage her to play a bit more every now and again.
Moving on. Our two new players are powergamers to the worst degree. I note that I define powergaming as somebody who only wants to get to the combat situations and ignores anything not focused on swinging a sword. I have recently broke these two of their habit by doing a couple things. Firstly, if they don't enjoy roleplaying and have actually tried it, not much you can do. But anyways, I had them roll their stats and place them in order as rolled. First stat rolled is strength, second is dexterity, third is constitution, etc. This means that they can't fall back into their most ideal rolls easily. True you can play a fighter with 10 str, dex and con, but its a quick way to die. Second, normally I do a 5D6, drop 2 but I decided to go with a 4D6 drop 1. This means that their rolls are lower. Third, I took away the "if its under 10, reroll" rule. Its easier to define a character if you can see their flaws easily. Next, I sat down with each player and told them to explain what their character history was and forced them to fill out a questionnaire regarding their character with small questions that helped them get a feel for their character. What do they hold dear? What are their pet peeves? Why did they take up adventuring? If they were a type of bread what would they be and why? (sounds funny, but that does two things, makes their character feel awesome, and if they laugh about it, the character starts to feel a bit more dear). Then the first thing I did was put their characters in a situation where they had to RP or loose quite a bit. They were found at the scene of an armed attack on a tavern by a evil adventuring group. The party looked very suspicious. They were holding bloody blades in a tavern with dead scattered about. All NPC's were dead. Nearly 20 guard had crossbow bolts focused on them. If they attacked, they were dead. And if they chose to attack, I would have ended the session and started rerolling characters. Then they had to deal with a series of complications in which they had to talk and act their way out. Whenever a character would do something that would violate their character, I asked them if thats what their character would do, or what they would do and then they took the hint and rethought their decision. They came out of the situation with an "apology from the city" which was a promise that if they managed to infiltrate the offenders they would get any property they owned. If they ruined the job, they would be put in jail to appease the citizens of the town.
The two powergamers have started learning to talk their way out of things. I added in some humor, a couple crazy/fun NPC's and they are addicted.
