Spring RTS Engine

Installing ubuntu onto a modern machine with 256MB+ ram and a CD drive using the pretty graphical installer. is fine, its easy, its quick.

Installing Ubuntu to a laptop HD in a usb caddy with a machine with an 8800 card making sure not to modify the main PCs HD at all, using a text setup program, then botting the 8 yr old laptop with the HD back in from a boot floppy, priceless.

I have ubuntu 7 running on my laptop now, and I have internet running (typing this post on my laptop)

However I cant install anything using command line, it keeps asking me to insert my ubuntu CD even though this machine doesn't have a CD Drive.

How do I get around this?