Hi,
I use a 2 GB 17 inch MacBook Pro for trading.
If you run bootcamp it is just like running a regular PC, it only looks better and there is hardly any fan noise

. It also has a great 1650 x 1050 screen and a built in connector for an external dvi screen.
If you run Paralells or VMWare it works well, but is notably slower, depending on memory and processor.
You can use it, but probably you will end up rebooting in Bootcamp if speed is very important.
Another alternative is running Quotetracker under Crossover for Mac. There is no Windows XP (or Vista) and very little overhead. It can actually connect to the Interactive brokers Platform running under Mac OS X.
Suitable if you don't track a lot of symbols, but less so if you flip through a lot of stocks.
I use this setup during the day to track and trade the FDAX, FTI futures and the EURUSD while doing other stuff under Mac OS X.
When the US markets open I switch to bootcamp (with XP) and trade stocks with Tradestation.
I like this setup as I mainly work with Mac OS X but only need a Windows environment for trading. It goes without saying I don't download or browse the internet when running windows...
