A 3rd party utility is going to be your "best" option.
If you need a single step solution using ONLY Windows components, you are going to need to:
1. Limit users to storing documents in specific folders.
2. Set a limit on folder size of 650 or 700MB.
3. Create a script or batch file to do the job.
If users have more than a CDs worth of data, you will need multiple folders and scripts.
All backups will be full backups as you have no way to log or mark files as backed up.
The built in CD tools in XP are far to limited to do any automated task.
In fact, the built-in CD tools on XP are a limited function version of Roxio's Easy CD Creator Basic version 5.
Your only other option would be to write your own backup application.
Chas