What soundcard do you have at the moment? And how much are you willing to spend if you need a new one? Do you need anything in addition to a soundcard, eg. software? What about a lead, do you have any xlr leads at the moment?
What mic? What soundcard? First, you'll need a preamp of some sort. Most built in soundcards have a preamp on the 'mic in' but those totally suck. Get an outboard preamp, like the Studio Projects VTB-1 and an appropriate cable to go from the mic to the pre and from the pre to the soundcard: http://www.markertek.com/CatList.asp?cat=CABLESCONN&subcat=AUDIOCAB&prodClass=&search=0&off=0
You could get a really cheap mixer, like the Behringer EURORACK UB502 and buy an xlr-xlr cable and a stereo mini jack-2 phono y lead, for around $40, and this will probably mean you wont need a new soundcard, if the one you have at the moment has a mic/line input. I did this(with the Behringer UB1204FX-PRO), and although the quality wasn't great, it still did for a couple of demos. If you have a microphone input on the soundcard, it will probably be pre-amped and the signal might be too much for your computer to handle(this happened to me). If this happens look for a way to turn off the mic boost thing. I'll will talk you through it, or attempt to if needed. Here is the mixer i suggested
(this is not an ideal solution, but it is a solution none the less)
The Shure has an XLR socket (mic cable connector) and your computer has a 1/8" mini plug.
The simplest way to get the shure into your computer is to go to Radio Shack with the mic and tell them what you want to do. About $40 later you'll have a couple cables and adapters and you'll be good to go.
A better soundcard ("audio interface" as we call them to distinguish them from the almost useless cards that come with computers) is the best idea. The preamps in your computer's soundcard or *horrible* as are the convertors. Head over to: http://www.m-audio.com/
And take a look at the products they have. That will help you start to get a sense of what the different options are and give you more specific questions to ask for narrowing down the best thing to get.
With the right audio interface usually all you need to plug in the Shure is a mic cable. You can get those at Radio Shack or just about any music store.