I have an Acer Aspire laptop, 2.2GHz, 2 GB DDR3 Memory, 250 GB HDD. And for the three races thing, found out I just didn't put Core last. However; when I have all races activated, and try to hop on a large map (to just see them get kicked by my colonial fleet) 4-5 minutes in it mini dumps.
You'll never be able to run all of the races with only 2GB of ram on that system I can do this with Effect settings on High/Medium/Low but the lag gets pretty bad if fleet sizes get too big on large maps, but I'll run between 1.4 to 1.6 GIG on ram usage (Highest and I'll mini-dump).
My system specs are i7 860, 8GB DDR3 Memory, GTX 260 (896MB).
Your available ram is only 1 GB or less depending on your OS and other running programs. I sincerely suggest you upgrade to a minimum of 4GB ram if possible. You might be able to load one or two of the races but I would suggest keeping Effects to High/Medium/Low or Medium/Low/Low depending on your memory consumption.
FYI, Colonials is the heaviest hitting race as it's texture and meshes are significantly larger than any of the other races in my mod.
I also have a version of the Optimization project that you may also want to try that can be stacked with my mod but I wasn't seeing any issues on my side in Diplomacy so didn't pursue it further. Let me know if your interested.