First of all, what do you mean by "normal preview"? For me (and every other AE user I know) RAM preview IS the normal preview. If you mean the spacebar, I never use it and I don't know anybody who does.
Actually, all of the FAQ will probably be helpful to you.
Since you're just starting out in AE, I suggest you start here.
If you want something a bit more in-depth, for only the price of a new video game there's this wonderful resource.
thanks for your help Szalam, i found that i had "render multiple frames simulutaneously" checked in memory & multiprocessing. unchecking this seemed to fix the problem but now im thinking that i may need to invest in some more ram. i only have 4GB.
Yeah, if you're using CS5 (or CS5.5), 4GB of RAM isn't much. I have 48 on my work machine.
Thanks for sharing. I also had the same problem.