Re-Map Launch Key
Open the following registry key:
HKEY_CURRENT_USER\Software\Microsoft\IntelliPoint\EventMapping
Open the Intellimouse control panel.
Edit the bottom button to perform the action you want and apply it. This will save its setting in the 6 subkey.
Rename 6 to 650
Now go back and reset the bottom button to your original command.
Map DPI buttons
You can't actually map the DPI buttons directly; they don't send the same type of commands that the other buttons do. However, you can get the last button pressed (consequently, the button that's lit up) with EventGhost
After you install EventGhost, open it and create a new file.
Add a new plugin
Select the Generic HID plugin, click Ok.
Select the Sidewinder mouse, then click Ok.
When you click any of the DPI buttons, EventGhost will now show an HID event. Note that if you press the currently selected DPI button, nothing happens. So you can only use this for events where the three buttons control the state of one object - such as the landing gear on an airplane.
Create a new macro in EventGhost, and assign whatever event you want to the macro. That's pretty much all there is to it.