I have a MJ that runs fine on XP pro with 500 mgs of ram. (Old Dell workstation, not wireless) I really can't see it being a ram problem unless you have a ton of 3d party apps also opening on start up. In the past I have had a problem with my second MJ on Windows 7 Ultim 32 bit.
I found it was a firewall problem, Win 7 would not allow MJ to start.
I'm curious what you find.