Hello wgfy,
The CD you are using is most likely a full or upgrade retail CD. These CDs will not accept an OEM product key, which is the type of product key printed on the Certificate of Authenticity on your Dell computer. The error message you are getting is exactly what it would say.
When you start your Dell, after the Dell logo is displayed and goes away, do you see a blue bar with
www.dell.com at the top of the screen for 2 seconds? If so, that means your computer may still have its hidden recovery partition. During the two seconds that you see the blue bar, press CTRL +F11 to enter Dell PC Restore.
If the computer does not have the blue bar as described above, then another option would be to order the Dell Recovery/Restore discs directly from Dell as described here:
http://support.dell.com/support/topics/global.aspx/support/dellcare/en/backupcd_form?c=us&cs=19&l=en&s=dhs&redirect=1
For great advice on all topics XP, visit http://www.annoyances.org/exec/forum/winxp