One thing you must do to upgrade to -current. Read the ChangeLog, and make sure how these changes will effect your system.
To rebuild your kernel you need to learn about your hardware. That is the key, along with knowing things such as the networking options. If you build kernels with a lot of modules, like Pat's, then you can get an idea what you're using by issuing "lsmod" (list modules). The longer your system has been up, and the more things you've done, the more modules you should see. That will give you a starting point to see which modules you are using with your Slackware system.
You can start learning by taking the .config file from a kernel you're using that works good for you, and then using that one to build a new kernel. I don't suggest using a 2.4 .config file to build a 2.6 kernel, though. For that one I'd print the 2.4 .config file and follow it as you build the 2.6 kernel from a fresh .config file.
You might want to do this with fresh sources for a 2.4.32 kernel
. You could use Pat's 2.4.32 config file
from -current as a starting point by following one of my simple guides
and putting that config file in at step #5 of that guide. Then between steps 6 and 7 you can run "make xconfig" and look at the options, changing just what you know is specific to your computer.
For instance, you can get information about your CPU by issuing "cat /proc/cpuinfo" and then you can change Pat's options to fit your kernel. Similar steps for the remainder of your hardware, such as removing support for every NIC except yours. This is a simple way to start learning your hardware, and how to rebuild a kernel.