Is this the built-in camera on the notebook itself? If so, make sure it is enabled in the BIOS (if such an entry does indeed exist). Dell does not list any specific drivers for the 1521 for Windows 7, but that should not be a problem.
Looks like Creative Labs makes the webcam and I am sure it is available via Windows Update. The issue now is to make sure your computer recognizes the hardware.
Check the BIOS first. It is possible that the webcam is defective. If so, Dell would have to help or you would need to buy an external webcam (unless you are up to replacing yourself).
Come back after looking at the BIOS. Good luck!