Scotsdude is right: In today's world, it is NOT about your mainboards, All the new mainboards support from 1.5 to 3 Gigs of RAM; It is all about the operating system.
Just as an experiment, and used Windows 98 SE for a test. I was building myself a New computer, I knew when I built this computer I wanted to run 1 GIG of RAM (not that I need it, it just sounds so much cooler than 768, which I had in my last machine).
It is a Pentium 4 - with the i850 chipset, so it is RAMBUS RAM. With Windows 98 SE, the computer ran, but was slow unbelievable flaky, I had to reboot (warm reboot manually with the reboot button on case) from 5 to 10 (sometimes more) times a DAY. Windows 98 SE was just helpless with that much RAM.
I set up another HD, and installed XP Pro, which I have used and liked since last July, and it runs perfect.
1 GB. My excuse is, to run a game server online. However, nothing else I could possibly think of would utilize that much RAM.
I am also curious to know what Mike *THINKS* he needs 1+ Gigabyte of RAM for. (I think this is another case of, "my brother in-law who works with someone, said, that Bubba who *used* to build computers said, etc.).
LAST: If I'm going to use that much RAM, in ANY computer that I build, it would only be the best mainboard, or a premium brand, such as Intel, Asus, or Supermicro. If you can't afford the extra $50 - $80 for a premium top quality mainboard, you probably are buying the RAM for the wrong reason.