Buy one... internal, USB, firewire, whatever you can afford...
or image them to HD with Alcohol and then mount them as virtual DVD's thru the Alcohol 120% UI. Latter option needs another computer with a DVD drive and Alcohol installed there as well- images can be transferred to the laptop via LAN.
You can also use daaemon tools which is free, but in that case you must image the DVD's with a compatible software. For video DVD's you might use DVD Decrypter in ISO mode, so you won't have probz with css protection or Macrovision.