Charting scientific data - Excel 2003

Every once in a while I need to plot some spectral data. Because it's not
very often and it's just simple plots, I can't justify to my boss the
purchase of fancy and expensive plotting software programs (SigmaPlot,
Origin, etc.). However, I can't figure out how to one thing in Excel:

I have data with x being time and y being some value. Also, there are many
points with y=0. I want to plot an xy scatter graph with a smoothed line
connecting the points. However, because most points are at y=0, most of the
plot is hidden by the x axis. Problem is solved if I set the y minimum at,
say, -2 but then the axis numbering starts at -2 instead of 0. How can I set
the minimum at -2 but have the numbering begin at 0?