Removing a DVD Image from a drive?

Hello everyone!

Recently I wanted to wipe my MacBook Pro, and do a clean install of Snow Leopard. However doing so proved difficult, because my DVD drive recently gave out and stopped ejecting disks (Had to open her up and take out the drive completely). Anyways, in order to do a clean install, I had to create an image of my Install DVD On an external hard drive, and wipe the computer in target disk mode from another mac.

The clean install worked perfectly, although now my external Hard Drive is stuck with the DVD Image of the snow leopard install disk on it. I would just wipe the drive, however it has about 450 GB worth of data on it (When I put the Install DVD image on the drive I chose not to erase the current data) and I would just get another hard drive to back up my data and reformat the drive, but currently I do not have another drive to transfer the files to.

I would just delete the Snow Leopard install disk files, but everytime I plug in the hard drive, it pops up like an install disk and its quite annoying. In the mean time the hard drive still works perfectly, its just annoying always having to close the "Install OS X Snow Leopard" window each time I plug in the drive. (Note: If I remove the install disk files from the drive, the Hard drive still pops up like an install disk when its plugged in)

So my question is this, (I know I'm finally getting to my point haha) is there any way I can remove the "Install Disk" image from my hard drive without having to wipe the entire drive? Or am I just going to have to get another hard drive to back up all my data and reformat it? Thanks for your help guys, looking forward to your replies.

Regards,
-LS

Other System Info:

~Computer
Model: MacBook Pro 3,1
Make: 15" Discrete Model
Processor: Intel Core 2 Duo (2.2 GHz)
RAM: 4 GB

~External Hard Drive
Model: Western-Digital My Book
Size: 500 GB (Capacity); 33 GB (Free)