Has the computer ever detected DVDs or is this a new issue? Please go to http://www.dell.com/support/troubleshooting/us/en/19/Product/inspiron-2500
and enter your service tag number. This will give you information about your original configuration.
You can also try the following:
Look under DVD/CD-ROM drives and look for DVD in the device name.http://www.computerhope.com/issues/ch000833.htm
An easier way is to look at the CD drive and see if it has DVD on it and if it supports DVD writing it will have something like DVD -R/+R or DVD Multi Recorder on it.