Several questions spring to mind.
You say you are going to buy a 750 ZIP. If you mean a 750 ZIP disk, make sure first that the ZIP drive in your computer will support 750. My Dell PC is just over 3 years old and the ZIP drive will only support up to 250.
You say you don't have a USB 2 port on your laptop. It doesn't matter.
If you only have a USB 1 port, you can still use USB 2 devices.
I only have USB 1 ports on my PC but I use a USB 2 pen drive to do my backups. No problems at all. It takes about 7 minutes to do a 450MB backup.