Hope this doesn't come too late, but, depends on outputs of your deck and inputs on sound card some possiblities..
rca L R out of deck to L R rca to miniplug cable to miniplug line in on computer adjust the volume with start menu accesories multimedia volume levels
if you are balanced coming out of the tape machine and don't have balanced ins on the computer you'll need a very high quality line level transformer to bring it from +4dbv to -10dbu any wuestion keep em coming...