Global maps in Robinson projections

Hi,

does anyone know of a way how to project a global rectangular lon-lat 
map into the Robinson projection?

For the rectangular map, I use as.image() to create an object plotable 
with image(). The grid-argument for as.image() comes from an 
expand.grid(lon,lat), where lon and lat derive from a Gaussian T42 grid. 
Vector z which contains my data at each  point of the Gaussian T42 grid 
contains NAs, for example over the oceans.

I manage to transform the original gridpoints to the robinson-projection 
(by spTransform() after converting the grid to SpatialPoints), however 
the interpolation of the data to this new grid fails (interp() from the 
akima library) because of the missing values in z.

Any idea would be highly appreciated!

Cheers, Boris.