This is most likely related to your source material.
Are you working with photos? Have they been optimized to no larger than 1000x750 pixels, per the FAQs to the right of this forum?
Also, as you're working is there a red line above the clips on your timeline? This is an indication that you need to render your clips. Too many unrendered clips can overload the program. Render often (and that red line will turn green).
As I said, you don't mention what type of camcorder your video is coming from, but some non-standard video codecs can require a lot more power to work with than more standard, tape-based camcorders.
System Memory is a broad term. It can mean the physical RAM, but can also mean the system's Virtual Memory (Page File).
Assuming that your RAM is not bad, say a bad stick, I'd look at your Virtual Memory. A couple of things to consider is how large a Page File is set, how it's managed and also where it's located. For editing computers, I set my Virtual Memory to static (fixed size and not dynamically managed by the OS) and at a size equal to 2.5x my physical RAM. In my case this comes out to a size of 10GB for my 4GB RAM on all machines. I also experimented with the placement of the Page File, and found the best performance to be split between C:\ & D:\ on my workstation and on C:\ (default) on my laptop.
Also, many unnecessary programs and Processes can rob the computer of resources, i.e. Memory. I follow the tips in this ARTICLE, for basic setup and then for starting an NLE session.
Hope that this helps,