Well, given the abstract simplicity of the D20 systems (yes, I know there is another thread on these forums that states otherwise) and the perceived complexity of Rolemaster in all of it's incarnations, I can definitly see where you may hit a snag. I have to admit, I have never had the need to persuade my players to play Rolemaster, in fact the difficulty at times (as a short break
) is to persuade them to play something else.
I can't help but feel that the complexity of the system isn't going to be your biggest hurdle, I don't know your players like you do, but I have been around a fair while, like you. I think your major issue is going to be getting your players into a system that they don't yet know how to turn to their favour (that's putting it mildly).
Personally, in your shoes, I would go for the most complex system, they are usually the most richly detailed. I'm a RM2 fa myself, so I can't comment too much on the newrer systems.
Now, how would I do it...? I remember almost 20 years ago, when trying to get my wife into a little roleplay
, I went straight for the kill, literally. In my own opinion the combat and spell systems are the show-peices of RM2, so I created a character, a Fighter, and drew up a little scenario than included an arena. With easy to beat opponents, and a couple of healing potions in the sidelines, I put the character through it's paces in combat. Seeing the full glory of critical hit tables, fairly simplistic maths and the results of a few fights can do wonders to sell Rolemaster, and I think, given the very abstract nature of roll-a-dice, add-a-number, see-if-you-hit, roll-more-dice-for-damage, add-a-number, rince and repeart until hitpoints = 0 in herent in D20 systems, Rolemaster comes out tops.
What I am trying to say, is that you should show your players how much fun RM can be and how the system itself can give a much more rewarding experience than plain, old dice roll-number games. You could even try selecting one or two individuals, show them the ropes and get them interested. Give them an easy time of combat, let them have some fun and then, like some kind of crack dealer, once you have them hooked, get
them to reel the other players in.