Read the forums or use the search function at the bottom of the page.This has been covered before.I am running on 256MB of RAM and I can get 20 fps or so.Here's a few hints:
Don't use too many dynamic entities in the same area.
Try not to use a large open area or even a large closed one.If you can see for miles it slows down your pc.
Keep outdoor stuff to a minimum.
I found my pc runs quicker if I make several small levels instead of one big level.For instance if I have a 3 story house with a basement instead of making it one level I can split it into four levels one for each floor and one for the basement.
Don't make super long halls/passages.If you do put bends/walls etc.
Bullshock has a free level viewer available that use can use in conjunction with the FPSC test level function that will help you see polygon leaks,etc.
Speaking of polygons,keep them fairly low.
If you don't know something search the fourms.If you are still unclear on what to do,ask.
There are other people that have been doing this a lot longer and are a lot better and kmore knowledgeable than I.Seek them out.
I am not going to say FPSC does not have its shortcomings.Part of the fun I have is trying to work around them.I can say that if it weren't for FPSC I would not be able to make a first person shooter the way I want to.I recommend this to anyone.
Not changing this sig until I get rich