Well, the original HDD works. I read over everything on the label and it said to move the jumper to a certain spot to put in into cable-select. I did that, put the Cube back together and booted with the option key down to try and install 10.0.3. When I did that, low-and-behold the internal drive showed up with some random name. Clicked on it, booted to it, and it came up running 10.4.11 Tiger but had some very, very, very, VERY GROSS pictures on it. I really don't want to go into details.
ANYWAY, booting into 10.4 now to wipe the drive. Hope to install 10.0.3 soon.