Help with Blender

I know that sounds kinda like an obvious title but its the only thing i coul come up with. Anyways my problem is that when ever i have to much in my scene blender crashes, and when i say to much it crashs if i subdivide a cube 3 times or more. I am new to blender and i really dont thinkl it should be doing that. i am on vista hp 64 bit and i extracted all of my files to C:\Program Files (x86)\Blender on my hard drive, i have more then enough power in my system to cope with this basic rendering, i am gunna write down my parts cos i know with some software it doesnt like certain parts. my video card is a radeon hd 4850, my mobo is asus P5Q and i have an E5200 @ 2.5ghz. any help would be apreiciated, thax in advance:D