Your eMachines is going to be very difficult to find upgrades for, considering it is running on hardware that's not even standard anymore.
By the time you find said upgrades, if you actually can, you'll still only have 2GB of DDR2 RAM (which is the maximum supported), a better but still incapable processor (unless you're playing games from 05'

, and maybe a larger hard drive. I don't know about graphics.
This computer isn't even worth upgrading, because even if you do you still won't be able to play modern games. I wouldn't even count on running TF2.