Driver and/or decoder needed?

Hey all...I took my dvd-rom out of an old computer and installed it on my other computer (an HP Pavilion with Intel Celeron), but it won't read DVDs. It does, however, read CDs. When I trouble-shoot the dvd-rom, it says it's working properly. When I try to play a DVD, I get the following message:

Windows Media Player cannot play the DVD because a compatible DVD decoder is not installed on your computer.

The player is a TOSHIBA DVD-ROM SD-M1302. I haven't had any luck finding the appropriate decoder. Any help would be greatly appreciated. Thanks!