Question: 3D plot with unequally spaced axis

Hallo,

I´m trying to create a 3D-plot of the following data

0.25Y               0.5Y               1Y               2Y               5Y               10Y

01/25/2000      0.0547       0.0557        0.0567       0.0554       0.0598         0.0610
01/26/2000      0.0548       0.0569        0.0578       0.0576       0.0588         0.0592
01/27/2000      0.0549       0.0570        0.0579       0.0580       0.5900         0.0610
......
12/30/2007      0.0210       0.0221        0.0257       0.0287       0.0290         0.0310

The data consists of term structures of interest rates (z-axis) evolving over time. The x-axis
shows the date. Unfortunately the times to maturity (y-axis) are not equally spaced. The
first rate has a time to maturity of 0.25 years, the second of 0.5 years, the third of one year and so on.

I tried to transform the data to a matrix and use "matrixplot" to construct the graph. Basically this works
well, but I don´t know how to integrate the x- and y-axis correctly into the graph. How can I add these into
the matrixplot command so that the unequally spaced y-axis is plotted correctly?

Thanks for your help.

Frank