I managed to get this working over the last few days and had noticed there was a lot of misinformation around about how one might do this. I tried following a couple sets of instructions before settling on the steps below and most of them didn't even really have much to do with the issues stopping it from working.
The big problem keeping it from running right away after install is that Slackware64 is a pure 64bit environment. It's not incompatible with 32bit software but you have to provide the 32bit libs yourself. The official distribution channel does not have such packages. The problem is actually very simple at this point: you just need to provide those libs and you're ready to start using the software.
Follow the directions at http://slackware.com/~alien/multilib/ to install multilib support packages for your version of slackware64. I didn't stop with the libs, I installed all the multilib support packages. At the time of writing there are several versions available including -current.
If you're using the nVidia driver you need to re-install it after this and tell it to install the 32bit libs. You may have told it to install them before you had the multilib packages installed. They'll be in an unusable state in that case which is why you need to reinstall the driver now.
After that you should be good to go.