Just thought I would post this ebay link to what seams to be a good deal on a SM57 mic and x2u preamp/computer interface combo. Most of them on ebay are $170-200 for the set but this one is $129.
I am in no way affilitated with the seller and don't know much about recording but I bought one to start capturing some pedal demos on my computer. I am sure there may be better options out there but this kit seams simple and easy to use so I went for it.
http://www.ebay.com/itm/Shure-SM57-X2U-USB-Interface-Instrument-Mic-SM57X2U-NEW-/370750214605?pt=US_Computer_Recording_Interfaces&hash=item56526f51cd