MB can also be a pain with your hardware too.

Z for the win, roll on V4.

As Jay said you need to sit down with a few of the free tutorials to get your going with it as it is a strange app to get your head round to start with.

Just got my PC going with vista 64 and lots of RAM and I dont have a problem getting to silly silly high poly counts 24million + in a single mesh with no slowdown at all.