I don't know why but It's always annoying to set up my mouse in linux.  Though it's not that difficult it takes some testing to make sure that it's working proporly.  So here is part of my xorg to get the scroll and the back/forward buttons working in slackware 12.2:

Section "InputDevice"
Identifier "Mouse1"
Driver "mouse"
Option "Protocol"
"ExplorerPS/2"
Option "Device" "/dev/mouse"
Option "Buttons" "7"
Option "ZAxisMapping" "6 7"
EndSection

Also you need to created a file called .Xmodmap in your home directory, which contains:

pointer = 1 2 3 6 7 4 5 8 9 10 11

And that is it, everything should be working fine. Your setup might be different though and to change the button mapping without restarting X you can use the xmodmap command. EX:

xmodmap -e "pointer = 1 2 3 6 7 4 5 8 9 10 11"