I currently have 256mb of PC2100 ram, but I plan on adding another 256 soon. I'm just curious about how much of a performance increase I can expect, if any. I have all the settings at the highest and use a 30m mesh of the US. I noticed that FS2002 takes up all of the ram when it runs so I'm hoping that it will make a difference.

It won't actually make much difference to the theoretical speed of the sim, fps wise. However, the larger RAM will mean that FS will be performing far less swapfile paging than would otherwise be the case. As a result of this, your system will need less resources to be allocated to hard drive I/O operations. You will thus get a small boost in CPU availability to the sim where it otherwise would have been required for hard drive I/Os. Additionally, your fps will be more consistent, with less stutters and small pauses.Adding more RAM is also a good time to look at the state of your hard drive. No matter how much RAM you have, FS will still be performing very small I/O operations to the hard drive. Even though they are very small, the effect can still be noticed. So make sure you have also have a good, current hard drive that has a low access time specification and isn't too cluttered with data (my rule is keep it below half full and regularly defragged). Otherwise you won't get the full benefit of the RAM because hard drive I/Os will still be letting the side down a bit.