Maybe I'm missing something (I'm a primarily a KDE user), but last time I had to do something like this, I just created a simple shell script which was named after what I wanted to see in the Gnome context menu:
~/.gnome2/nautilus-scripts/Convert\ XLS\ to\ CSV...
with the contents performing the action I required, so something like:
#!/bin/bash # Convert XLS files to CSV... notrailspace=$(echo "$NAUTILUS_SCRIPT_SELECTED_FILE_PATHS" | sed -e 's/^ *//' -e 's/ *$//') sh /usr/bin/xls2csv "$notrailspace"
should do what you want (not tested tho). I needed the extra sed gubbings for the command I was calling, but you might get away with removing it, depending on how xls2csv works. Don't forget to make it executable.
The above isn't perfect, as I don't think it will differentiate what files you have selected and then only show when you right-click on XLS files, which might be possibly if you read around.
Peter.