Short answer: It's a POS, and it's started breaking after 3 years of pretty easy use.
Long answer (which is kind of neat, and also lets me know how to solve it): There's either crud on the lens of the CD, or it's scratched or otherwise failing, so it's having trouble reading the disc that's in there. The thing is, it keeps trying, spinning up the disc either every minute or continuously to see if it can get a read on it. Because it's 'active' it won't eject the disc, even when you ask it to through Windows. Windows used to time out when it failed to read a disc, but not any more.
The trick to getting the disc out is to do it while the computer's on but before Windows gets ahold of the hardware. Reboot, and while the "Dell" screen is still up, i.e., the hardware is powered but Windows hasn't fired up, hit the manual eject button.