If you need to check the ram on your machine and you happen to be running gentoo:

pddb-a01 linux # emerge -p memtest86

These are the packages that I would merge, in order:

Calculating dependencies ...done!
[ebuild  N    ] sys-apps/memtest86-3.0-r1

and then add this to grub.conf:

kernel (hd0,0)/memtest86/memtest.bin

Reboot and the choose the memtest option.