well, you could put a microphone on each practice pad (very close), record the hits to several tracks and then make it sound like drums with drumagog, or something like that, but i don't think the results will be very satisfying.

you'll need a trigger-to-midi interface to record midi-drums. it's like a drum sound-module but without sounds, so you just plug your pads into the trigger inputs and it generates midi data which you can send to your computer.

building drum pads from practice pads isn't as easy as it might seem. i'm sure they will work, but i'm also sure they won't work the way you like them to. manufacturers spend years of research to build pads that are playable and precise. they may look like practice pads, but believe me there's much more to it.
i'd get some pads on ebay. they're not as expensive as you might think. but i wish you luck, anyway!

hope this helps

You could use a Alesis IO with your pads to get the midi
http://www.musiciansbuy.com/Alesis-Trigger-IO-Electronic-Percussion-Interface-TRIGGERIO.html

Or you could just use an Alesis control pad like this:
(Dead Link Removed)

Just picking on the Alesis stuff because it is cheap. I don't recall but there was another trigger pad with midi for around $99 that you could get a Wal-Mart or Target I believe but don't recall details.

For more info on e-drums and how to DIY visit www.vdrums.com