Not sure if Mac Prime does.. It does however offer leverage (margins) on stocks..That can be found here. So as long as you have enough cash in your account to cover the so called (blocked cash) while the trade is active then you are fine.
To give you an example, lets say you have $20,000 in your account. If you wanted to buy 1000 BHP @ $38, it would cost you $38,000. Of course you don't have $38,000, however with the margin lending BHP's marginal rate is $10%. So, when you have executed your trade, you require the fund amount of $3,800 which then reduces your trading balance down to $16,200 until the trade is closed.
What I didn't like about Comsec is that if you didn't have a portfolio, then you could only execute a certain percentage in trades based on your balance. I could never work the system out exactly, but it certainly wasn't for me. In fact it cost me on several occasions. Hope that helps.
