Edit the file /boot/grub/menu.lst and delete or comment out the lines associated with the kernels you want to remove. For example, if I wanted to remove kernel #8 from my boot menu, I woud delete these lines.
Code:
title Gentoo 2006.0 (2.6.16-DAR-8)
root (hd0,0)
kernel /gentoo/gentoo-2.6.16-DAR-8 ro root=/dev/hda7
savedefault 7
This won't remove the kernel from /boot, but it's always good to keep an older kernel that you know was working around for just such an emergency. That's why I would recommend just commenting the lines if you don't want to see them.
You should start a new thread for your other, unrelated question.