I doubt your computer even recognizes the external CD drive until you actually get into windows. You might check in the BIOS and make sure "boot from other device" is enabled. Other than that, you might try using a startup disk to boot, then seeing if it will recognize your CD ROM. If it does, and you get through the initial copying over of crap to the HD, you should be able to complete the install no problem.

Might just be easier to borrow a CD drive from someone, or just go down and buy a cheapo internal drive.