I'm currently using a ProBook running 10.6.6 and if you'd like to use MetaTrader4, it is possible. Here's my own experience.
I've downloaded WineBottler, (go to
http://www.winehq.org/ or
http://winebottler.kronenberg.org/ ) .I believe they are the same thing. It's a free application that runs Windows applications without turning your mac into a windows computer. That's all to techie for me, but you can get the info. from the site. When you download it you will find MetaTrader4 as one of the pre-installed prefixes (their word for applications).
I'm no expert, I got this through trial and error. The only other alternative would be to buy Parallels and Windows 7 and run that on your mac.
It's worked fine for me. Hope this helps.
RD