There are several ways to get Xorg configured.
If you use kde 3.2.x there is also graphical tool under control-panel

in commandline i did first xorgconfig, witch is very similar to fx86config, but you can also do it with any text editor.
Choose monitor horisontal and vertivcal refresh in manual way and enter them as specified by manufacturer

for example for my Samsung NF959 monitor i do enter:
horizontal 31.5 - 110.2khz
vertical 40-160hz

xorg under slacware10 choses by default safe 1024x768, so you can add 1280 or higher resos as you monitor support them.
choose default depth 24 or 16. I do this by manual edit on xorg.conf file

also add Option "ZAxisMapping" "4 5" via editing saved conf file,
directly after protocol and device lines on pointer section.
In my primitive ps/2 wheel mouse with 3 buttons i have to choose protocol imps/2 and i do not need to specify option 5 buttons, it works and scroll after x restart well.
I have mentioned that sometimes it needs trying between auto and imps/2 protocols to make it work