[Gdal-dev] Black border (null value) after changing projection: possible to remove this?

[wqual]

Hi gdal-list,
Recently, I had to change the projection of some satellite tiles. I used 
gdalwarp for this purpose and it worked perfectly. 
The only thing is: as the tiles were rotated a little bit, black triangles 
(representing null-values) appear because of the rotation).
When I load these tiles in one view or a mapserver map, these black triangles 
overlay adjacent tiles a little bit. 
Therefore my question:
Is there a possiblity to remove these "triangles" resp.: can I define them as 
transparent? I would like to put them into a mapserver map using gdaltindex.

I would be grateful for some comments about this.

Best regards,
Wolfgang