I just recently installed Slackware for the first time after some bad experiences with Mandrake, Gentoo, and Fedora Core. So far I seem to like it more then any of the other distros I've tried, but I have to things that keep me from really being able to us Slack as my main OS over XP.

First of all, I can't get a higher resolution that 1240x768 even though my monitor and video card (Nvidia FX5200) will both go higher. I've been able to use 1920x1440 on XP, Mandrake, and Fedora before. I downloaded and installed the latest drivers from Nvidia, but the only thing I notice different is the Nvidia splash screen before KDE starts.

Secondly, how do I get my mouse wheel to scroll?

Regarding the video resolution try to see if your refresh rates are correctly set they vary according to thle resolution on some monitors.
The wheel of the mouse can be easily enabled by editing your /etc/X11/xorg.conf file, take a look at this forum there're a lot of posts about this and it's also said in X.org's doc files.
It was something like "Option" "ZAxisMapping" "4 5" in your mouse section on that fille.