I think it should be mentioned that not all modules that exist in the current Slackware install for various hardware devices are commented in the rc.modules file.
I had to do a little research about my hardware (always a good learning experience... that's why I love Slack) to find out what chipset my sound card uses. I had to add a reference to /sbin/modprobe cs46xx for my Hercules Game Theater XP.
So, i don't think it's necessarily as simple as scrolling down the rc.modules file and located the brand name of a particular sound card or modem or whatever....
...unless you have something that was hugely popular five years ago like Sound Blaster Somethingrather and is well-supported under Linux.
Is there a database of rc.modules or XF86Config files out there anywhere? I can see how something with 10,000+ lines of commented text with references to ever hardware supported by the current Slackware distro. could possibly help newcomers....
But then again... it could be argued that configuring a system with Slack isnt supposed to be easy