It's in the kernel, but it's horribly unreliable with older kernels. I'd suggest that you install at least kernel 2.4.18 if you're going to use that card as they worked a lot on that driver. Alternately, there may still be the driver on Intel's web site. The one in the kernel is called "Ether Express PRO 100" I believe. Since it's Slackware, try running netconfig as root and see if you can get it to pick up your NIC.
