First of all, this topic should be on the Slackware forum.
Second, what instructions did you follow? Were they Slackware specific, or general in nature?
The easiest way, assuming you are new to compiling the kernel, is to install the Slackware packages for 2.6, then just take the default configuration and build from that.
Come to think of it, did you see if your hardware is supported in Slackware's 2.6 kernel?