CoD4 Trouble with 5-Button Mouse!

So, I recently purchased a MicroInnovations wireless laser mouse (model PD7250LSR) and I'm having issues getting the side buttons to work with Call Of Duty 4.

The three 'traditional' buttons work fine, however buttons four and five will often not work. Sometimes neither will work and sometimes only button four will act up, which can be a pain seeing as it's my reload button.

I looked on MicroInnovations website but couldn't even find the mouse listed, much less find a driver update.

Usually, if I restart the entire PC the mouse will resume correct function at least for a while. There doesn't seem to be a button-combination that makes the issue occur, as the issue sparks up randomly.

I'm on a pretty basic XP PC.