I recently setup a customer's machine similar to your's. Maybe the info below will provide some starting points...

Three "holes" for disks...just a "guess" here..

1. One hole/tray is for the dual layer DVD burning drive. You can create and burn DVD movies or burn backup dat on to DVD disks. CLICK HERE to read how Dual layer burning actually allows you to burn twice as much data onto a DVD as the standard DVD burner and disk. Dual Layer also requires special DVD disks if you're going to use the dual layer procedure. Normally, this particular drive will also burn CD's with music or back up files as well..You'll also need the appropriate software to burn DVD's and CD's, but usually the software is provided with the computer.

2. The second hole/tray is normally a DVD-Rom or a CD-Rom which only "plays" CD's or DVD's. (The machine I set up had a CD-Rom drive in this "hole".) If you're going to be installing programs or playing music from a CD, this is normally the best drive to do it in..Although not guaranteed, it's probably the default "auto run" drive as well.

3. The third hold/tray is probably the floppy disk drive.
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Theoretically, then webcam should work...But...If you have an older webcam, you'll need to check to see if it is Windows XP SP2 compatible..It may or may not have software which would allow installation on the new computer. If your current software doesn't support Windows XP, check the webcam manufacturer's site and maybe they have updated software for XP.
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The Norton antivirus free trial can be uninstalled from the "Control Panel/Add-Remove Programs" section. So can the McAfee Security Center. If AOL hasn't been activated, it should also be relatively easy to remove from the computer at this time.

Hope this helps.

Grif