USB 2 external CDRW are backward compatible to USB 1.1, so it will work, just very slowly.
PCMCIA has a multitude of options. You can get PCMCIA miniature hard drives for backup as well as all kinds of other devices.
Have you considered a USB external hard drive for backup, or do you have to have a CDRW ?
I only ask because you can get some very large capacity external USB drives that work with either USB 1.1 or USB 2.0 and in terms of available storage space for your money they take some beating.
Every USB 2.0 external CDRW and hard drive I have seen so far is backward compatible to USB 1.1 although I have no doubt that somewhere out there you will find some that are only operating to the latest specification.
Dabs.com have a range of external CDRW and hard drives, as do most other mainstream component suppliers. Your local PC World also stock them as well.
You could do worse than take the laptop to a PC World store and specify what you want. Last week I was in my local store and I know from memory that they have a large selection of external hard drives, PCMCIA disks and several external CDRW drives as well.
The biggest problem will not be in finding a device that works with USB 1.1 or PCMCIA. Finding one that supports NT will be your challenge.