So... i getting windows OS on my imac, so should i wait till that happens in a few months, or buy portal 1 now to tithe me over until then? (I would buy it from steam)
Portal 1 works surprisingly well on OSX. You can buy it now, play it on OSX, then when you get your Windows OS installed, download it again and finish up where you left off.
Portal 1 won't last you that long unless you plan on speed running to perfection on top of everything it has to offer. However, it is worth every penny you spend on it :)