Both HD-DVD and blu-ray drives are backwards compatible with DVD and (I think) CD. I'm not sure what value keeping the original drive would hold.

Cheers,

Surround Music Fan/Computer Geek/Curmudgeon in training.
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861v4, HD621, Panasonic BD-P55K, Toshiba HD-A35, Oppo HD990, Dish Network 622, Pioneer DV-668AV-S w/ DVD Upgrades mod, EW Fontaine II (x5), Velodyne DD-15 (x2), Seymour AV Ice blocks (x7)