Buying a CD-Rom drive.....

You will need a quad speed or faster drive (600Kb per second).
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An IDE CD-Rom drive is a good idea since it shouldn't need a separate controller card.
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The drive should support multi-session Kodak Photo CDs.
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If the drive isn't IDE, can you use your sound card as a controller?
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Tray-loading CD-Rom drives are less fiddly than caddy-loading drives.