Hi Info,
The case with my computer is that it isn't really up to what I'm asking from it. Your case (4 GB of RAM, enough processor capacity) in not 'exactly' the same, so may Paul has better suggestion for you, but I'm happy to tell you what I did to circumvent the problem.
To be clear: this 'procedure' works for me on Windows XP. I do not know anything about Mac's, except that they do most of the time hat they are intended to, and even for that, I do not have any personal experience.
In Windows you start the task manager (right click on taskbar -> Task Manager, or start -> run -> taskmgr [enter]).
Go to the 'Processes' - Tab.
Select the process named 'ViennaEnsemble.exe', right click -> Set Priority -> Realtime. A warning appears: click 'Yes'
To revert the priority, same procedure except that you must choose 'Normal'
I hope this will work, although I hope Paul comes up with something better.