This post will assume that your problem is exactly that which you've found. Sorry if it seems a bit patronising, I've tried to keep it as basic as possible
Ok, first question: Are you using the 64-bit release candidate? If so, then have a pat on the back and then the rest of this post will mean something. If not, post and then we'll work from there.
Essentially, Supreme Commander is not set to be 'aware' of more than 2GB of what is called Virtual Address Space.
Possible reason? Well, it'll also be running on 32-bit Operating Systems which, by default, only 'use' 2GB for applications. This can be increased on these Operating systems to a point, but it is limited. That is what most of the post which you found is about.
However, you are part of the glorious 64-bit master race, therefore you dont have to worry about increasing the size of the total Virtual Addressing Space because it goes up to a possible
8 terabytes.
What
you need to worry about is the fact that the program is not aware that it can take advantage of this vast potential. This is actually the final step in the solution linked to on the GPGnet forums. What you will need to do is add a header to the supcom exe file that will effectively allow it to use more of the Virtual Address Space. The poster has kindly given us a .bat file to help us to do this with two clicks.
His link is down, but later on in the thread he gives an alternative link which still works. Here's one:
http://www.megaupload.com/?d=DDMJA8X0
You will get a compressed file which, once unzipped, will give a load of applications, a useful readme, a .dll file and a batch file called Startme.bat. This is the batch file we'll use to add the /LARGEADDRESSAWARE header to the supreme commander exe, which will then allow us to take advantage of the extra Address Space.
So, once you have unzipped the contents to a temporary folder,
Step 1: Make a copy of your
supremecommander.exe file (Ctrl-C, Ctrl-V). I normally save these files as
xxx origin.exe. So here you could call it
supremecomander origin.exe. This is so that if something goes wrong we can easily restore the original exe without having to reinstall the whole thing.
Step 2: Copy your
supremecommander.exe file (leaving your new backup copy to rest in the supreme commander/bin folder incase needed) to your temporary folder where you put the startme.bat. When you run Startme it will look for the .exe to be in the same folder as itself.
Extract from the readme:
Now for the tool to enable the supreme commander exe to use more than 2GB...
*** Important: First make a backup original of you supremecommander.exe, by renaming the copy to supremecommander.exe.original ***
The tool will add the "LARGE_ADDRESS_AWARE" header for you to your executable.
Copy supremecommander.exe to this folder.
Doubleclick startme.bat then the menu walks you through.
1) Hit the A key to add the large address header.
2) press any key to continue.
3) When back at main menu click 'v' to output the headers in text so you can see the values.
4) Now you can check to see if it is enabled. Scroll to the top and look for section "FILE HEADER VALUES". Look for a line in that section that says "Application can handle large (>2GB) addresses". It's the tenth line down in that section. If you see that line then the executable is now enabled for >2GB, you are done.
5) Copy the enabled supremecommander.exe back to your supremecommander\bin folder.
6) To avoid any strange issues with future patches, I suggest you rename your 3GB capable supremecommander.exe to something else like SupremeCommander3GB.exe, then make a shortcut to it on your desktop. In the meanwhile, keep the original where it belongs and you will avoid any possible patching or online issues. If you do want 3GB capability against another player then you will need to have the 3GB executable named as the original supremecommander.exe (keep a backup of the original).
I hope this gives you some kind of easier insight into the nature of this proposed solution. Good luck
EDIT: If you're interested, there are some nice articles on the MSDN:
http://msdn.microsoft.com/en-us/library/aa366912%28VS.85%29.aspx, or there's always wikipedia
http://en.wikipedia.org/wiki/Virtual_address_space
