well running 1 gig memory on some mother boards is quite an experience.
I finally got my P4 to boot a LOT quicker with using mem=1000M at the end of the second line in the grub.conf for the kernel you usually boot into.
It was the same old story--slow booting time--measured in 10's of minutes!
But since I really wanted to use at least most of the gig of ram, I used the mem=512M to test the memory caching/limit "fix" out.
And then used mem=999M and that worked, and then tried mem=1024M which did not work, BUT using mem=1000M does work!!!!
and using the free command gives me 1011428 total now and it flies!!
As usual your milage may vary--YMMV..
Hummmm--now I wonder if using the hugemem kernel/module would help???
At least I have 98% of the installed memory working now.