They do have external drives and burners but you pay a premium price for the
privilege of having it sit on your desk instead of inside the computer box.
Now that you say you have 4 GB free HD space you may want to consider a new
primary hard drive and use the current one for back up. A hard drive is
really (typically) easy to install.
But there is a certain appeal to having a portable burner. (That is what
made me buy an external Zip drive about seven years ago. I thought it
would be a great way to transport files. ....It has not moved from the place
I put it seven years ago ~:( ...So much for portability)