While the stock Slackware distro will run on a dual core computer, it will recognise only one core and only some of your memory (up to about 800MB). Presently just about any installation that uses the stock 2.6 kernel will need the kernel to be recompiles to take advantage of features.
The friendliest kernel compile guide I've found is this one
http://www.slackware.com/~alien/doku...kernelbuilding from Eric Hameleers.
As daunting as recompiling sounds, it's not that hard if you do a couple of things. First, do an oldconfig so you start with the config file from the stock kernel. Second, make sure your files system (Reiser, EXT3) is compiled in and not as modules and last, keep a backup of your current kernel so if the new kernel is broken you can boot the machine.
Dennisk