Mike.Looijmans@nym.sc.philips.com has provided the following circuit for an audio amp suitable for interfacing a moving-magnet cartridge to the line input of a sound card. The figure is for one channel of the stereo pair.
For capacitors, 222 means 2.2nF, 123 means 12nF, 100 means 100nF. For the opamp, use a 5534, or a 5532 (dual) if available. They're the same circuits: the 5532 has two 5534's in one case (cheaper & better synchronized L/R gain). Add in/output capacitors (suggest 1uF) to in- and/or output if you get a DC offset. You'll need a symmetric stabilized power supply; I suggest +/-12V. You can built one using 7812/7912 IC's, or you can use two 9-Volt batteries. Minimum is +/- 5V power. Current will be around 3-10mA, typically 4mA.
He has also provided a neat little preamp for low-level input: 
Thanks, Mike.