You can use System Information. Start -> Accessories -> system tools. Then expand components and select CD-ROM. Now your firmware should be in the Value to PNP Device ID. It will say something like Device ID IDE\CDROMLITE-ON_LTR-16102B______________________OS0K____\5&2DFCC752&0&0.1.0
see the bit in the middle of the _ OSOK thats where it tells you your firmware.
You could also use nero or other burning software to tell you your firmware.
I remember windows 9x showing you your firmware in device mamnger, but they seem to have removed that from xp for some unknown reason.