Hey guys...about to buy a Asus GTX 670 Direct CU II card and a Antec 300 case (my desk will only hold a case 48cm high and 22cm wide)
I was wondering if the card will do well in this case in terms of air flow and size? and if thats no problem, then is SLi a possibility in the future? because this will make a difference to what PSU i buy

I've got an antec 300 and a gigabyte windforce 670 which is similar is cooler design to your card.

With all my case fans on minimum and farily poor airflow as a result, before the card arrived I thought I would suffer high temps due to the gfx card not exhausting heat out of the case.

Turns out these cards produce hardly any heat or the coolers are just very good - max temp it gets to is about 62c on auto fan profile, so I wouldn't worry.

SLI I imagine is a completely different story.