Hi, it's very easy, you need a USB or Firewire audio interface, either of these, or similar will do....
http
/www.m-audio.com/products/en_us/FastTrackPro.html
http
/www.alesis.com/io2
http
/www.focusrite.com/uk/products/saffire/saffire_6_usb
In my opinion the M-Audio is the easiest to use and set-up, just load in the software, and plug it in. It will give you two mic inputs, with phantom power, and a couple of line inputs, all you need to record your drums in stereo, and overdub if you like with virtually zero latency. If you have any problems just post back and ask me, but seriously, this is no big deal, these boxes are so easy to use these days, it's up to you which one you go for, but they all do more or less the same job. You may want to download a free recording application like Reaper (optional license) to get you started, which is one of the best and most friendly to use DAW's around these days.
Purplepatch.