Often when I set a 'particle per second' amount or something similar that is too large, After Effects will freeze on me for a while. Is there anything that can be done against this?

What are your system specs? In most cases you can improve performance by upgrading the RAM or CPU. I had similar issues with running AE on my Dell 8400, P4 3.0ghz machine. Now that I run it on my new Dell Precision 490 with dual, dual core Xeon 3.0ghz processors there is hardly ever a pause of any kind in processing, at least not until we get to rendering, that is a different story

Thanks, well my specs are:
Processor Type and Speed:AMD Athlon X2 4000+ @2,4GHz (AM2, Brisbane)Amount of RAM:2048MB 800MHz DDR2 (Dual Channel)and a 7600GT videocard. So, well there okay I guess.

Nice CPU by the way, Dual Core 3GHz

The X2 4000+ is a dual core 2.1ghz processor, still should do a good job with After Effects.
That is the same as my laptop and it does a pretty decent job most of the time. You have to remember however that some effects require some intense processing.

There are two CPUs on my machine, both are dual core Xeon 3.0ghz, lots of power

Oh yeah, I misread. Four cores, well that will at least save some rendering time!

Yeah, my CPU normally runs at 2.1GHz, but I had to overclock it to sync it with my RAM, so now it runs at 2.4, hehe.