:-/
Unfortunately i'm in the same boat... I want to be able to send e-mail using my MobileMe account using a non-MobileMe alias. I even own the domain in which i want to send from. I'm probably not going to renew my MobileMe service because of this.
I did what DavidFL did... It's as good as it gets... I hate not having all my email in one location though, having to send from another mailbox sucks.
Alex