You would probably be happier replacing the optical drive with an SSD. That way you can get away with a smaller SSD and have the old drive or a new 500 GB hard drive for storage.

Here are three SSD drives:

http://www.ifixit.com/Mac-Parts/MacBook-...

Here's the enclosure:

http://www.ifixit.com/Apple-Parts/9-5-mm...

Here's how to install it:

http://www.ifixit.com/Apple-Parts/500-GB...

As little as I use a optical drive, an external USB/Firewire dual layer LaCie LightScribe drive works great for me.

http://www.lacie.com/products/product.ht...

or you can put the existing optical drive in an external enclosure like this one:

http://www.geeks.com/details.asp?invtid=...