go to any store that sells oem pioneer dvdr drives and get either a 107 or 108. the 108 is dual layer. then just follow that owc guide.

I say pioneer because they work so well with apples hardware and are fully supported by the os and iapps.
Mac mini C2D 1.83GHz - 2GB RAM - 200GB 7200rpm HD
Sawtooth w/G4 1GHz - 1GB RAM - SIIG SATA w/2x1TB HD
B&W w/G4 600MHz - 1GB RAM - 2x80GB HD
Sawtooth G4 400MHz - 512MB RAM - 40GB HD
Dell Ultrasharp 2007WFP 20" Widescreen LCD
2.94TB Total Storage