Howdy Lapslide guy,
It has been my experience that humbuckers drive good enough to just plug directly into the microphone input on your sound card, and use software controls to regulate volume. So far as the Piezo-electric pickups I think the same is true because the microphone input is looking for a lower input signal than you might get from a line level source. If you are bringing in another source like from a cd player using the headphone jack and a jumper cord 1/8" TRS male-male, you would want to use the line in jack on your sound card because the driven signal is wanting to see a 16-32 ohm load which may be too much for the microphone input. You will also likely need a 1/4" mono female to 1/8" mono male adapter to plug your instrument cord into the sound card. readily available at Radio Shack for less than $3.00.
Works on guitars that I own and should work on your lapsteel as well.
Have fun with your music.... it just gets better!
Take Care; Doug
"what is this quintessence of dust?" - Shakespeare