Run the Crucial scan and see how much the motherboard will take. I'd also run Belarc then look up the motherboard and confirm the max memory.
With a 32 bit operating system TS2010 is limited to 2 gigs, however Win 7 should come with a 64 bit disk so you can just reinstall. Currently on your system Win 7 takes up 512 mb of memory leaving 1.5 gigs for Trainz. Win 7 32 bit can "see" roughly 3 gigs of memory, 3.5 on some motherboards if you are lucky. To see more memory you need to move to WIN 7 64 bit which can "see" at least 64 gigs if your motherboard supports it.
Cheerio John