There's only a select few types of file which are supported. Currently these are jpg,jpeg,gif,png,tif,tiff,rib,sl,zip. To upload a set of files, please use zip. This will allow the files to be opened on most platforms easily. There are issues with tar files and the wiki, whereby certain browsers will try to open pages ending in tar as a tar file.
To zip a whole load of files like you would for a tar file, use
zip -r zipfile.zip directory