Now I know you were intending to try and install something like 8 to 16 Gig's of system RAM, that's good, but your motherboard will not support that. But all is not lost because of this fact for something you said. You said that after this upgrade you were planing on installing Linux, I hope it will be Ubuntu, for that is what I use and let me tell you, the 4 Gig's that your system can be upgraded to is nothing to sneeze at. I have Ubuntu installed as my primary O.S. on all my computers, 1 server, 1 desktop and 1 laptop, all those computers are running 4 Gig's of RAM only and are doing just fine with 4 Gig's. To be honest with you, I think I've only toped up to around 1.5 Gig's of system RAM ever being used at any given time on any of my systems, it's almost like the extra 2.5 Gig's that aren't being used is a waste. Heck with Ubuntu and the way it manages it's system memory, I only use approx. 350MB's to 425MB's when my systems are idling. I've seen my systems only chum on approx. 500MB's to 675MB's to maybe 700MB's under a lite load. Again, that's getting no where close to using up 4 Gig's of system RAM, no where close!
So if 4 Gig's is all your motherboard can handle, and you truly intend to run with a Linux distro, than your going to be just fine, install the 4 Gig's and install Linux and everything will be peachy!