I had a Sparcstation 4/330 with optical mouse, without the pad.  Of
course I wanted one, and eventually found one, but in the interim, I
did what an old hack suggested and printed myself a grid on paper.
Works peachy.  The spacing of the grid will determine the tracking
speed of the mouse.  Graph paper works if you get a fine grid.  Try
.5cm.
Just to get you on the road til' your pad gets to you.  My old hack
told me they had a problem with the pads disappearing and had a file on
their network for folks to just print themselves one for the day.
Jeff