Both Shard and i have posted numerous times about stocks and software, try looking for some of those posts using the search feature.
As i mentioned in one of those posts, there are professional trading solutions out there for Macs, but they are very expensive just like they are on the Windows side. You can easily daytrade without any fancy software. All that software is going to do if you are a beginner is cut into your margins with high rates and confuse the hell out of you with a ton of options, indicators, oscillators, retracement tools, etc.
I recommend that you set up an account with an online broker like ameritrade or etrade that has free real-time quotes and charting. Daytrading is all about charting and predicting reversals. The only things you need to do this is real-time charts, fast order entry, a few simple indicators, and patience.
I have daytraded for the last 5 years and actively trade options, and all i use are some free charting services for long term charts, ameritrade's real-time trading software (free to all clients), and the knowledge i have gained from reading lots about candlestick charting, patterns, and resistance/support.
Read up on simpe technical analysis using candlesticks, learn the patterns and what they indicate, and figure out resistance and support levels for the stocks you want to trade.
You should find a small number of stocks that you can easily keep track of. They must have good daily volumes (>1mil) and be volatile enough for intraday trading.
If you have anymore questions please ask.
Here are some sites that where you can learn more about charting and screening for patterns:
Stock Charts.com - has lots of great pattern screens for free, and a large collection of educational material
StockConsultant.com - helps easily identify key support/resistance levels
