Hi Ryan,
Having a strange problem trying to install Debian AMD64 (downloaded the latest CD). I run through the normal installation, partition my drive (79.5MB ext3 /, 512MB swap), all goes well, I reboot and GRUB hangs at "GRUB loading, please wait...". I've checked /boot/grub/menu.lst and it looks fine to me.
I had exactly the same problem with my notebook. The partition size did not change a thing and the WinXP install CD crashed each time I tried to boot and the HD was partitioned. Partion Magic was not able to boot, due to that failure. Interesting was also, that a Debian 32bit was not able to write the mbr (lilo and grub, grub had the same failure as you have), only Knoppix worked out. After some tries to reinstall my Debian amd64 it once worked out. Thats how I solved it - try reinstalling.
Greetings, Tobias