first off, the "proper" way to transfer from a dat or other digital medium to a computer, etc. is "digitally" (i.e. preserving the integrity of the zeros and ones originally recorded to dat).
Unfortunately, by itself, the D100 does not have an internal digital output for doing this. The digital data can, however, be exported from the d100 via a proprietary cable that attaches to a small rectangular jack on the bottom of the d100 (commonly called a 7 pin connector). Does your friend have one of these connectors?
If your friend does have 7 pin connector with a digital output, then you'd need to have a soundcard (or usb device) capable of "reading" the digital data being fed to it (called a digital spdif signal) into your computer. Not all soundcards are created equal for this task, so if I haven't lost you yet, happy to follow-up with further suggestions/clarification.
Bottom line, however, without a the 7 pin cable with a digital output and a computer soundcard capable of accepting a digital spdif signal, you're only going to be able to transfer dats to your computer using an analog cable. This will definitely compromise the soundquality of the recording since it will be different than (inferior to) the pure digital master recording you started with.