To connect a professional microphone that uses a 3-pin XLR type output connector to the 3.5mm MICROPHONE jack on a computer, we recommend a particular adapter cable that will distribute the mono signal from the microphone to both the left and right sides of the computers stereo microphone jack. The adapter cable is the Hosa brand model XVM-105F, 110F or 115F (available in 5, 10 and 15 foot lengths). Since the line is unbalanced, keep the cable length as short as possible to reduce the pick up of any noise.
Alternatively, you could connect the microphone through USB. This will require an XLR to USB adapter cable such as the Lightsnake brand USB microphone cable. Be aware however that if you are monitoring the mic audio, there will be a slight delay (know as digital latency) from the time you speak into the mic and the time you hear it.