You can also help aolserver by adding mime types in the ns/mimetypes section of your configuration file:

ns_section "ns/mimetypes" 
ns_param   default         "*/*"     ;# MIME type for unknown extension. 
ns_param   noextension     "*/*"     ;# MIME type for missing extension. 
ns_param   ".xls"          "application/vnd.ms-excel" 
ns_param   ".doc"          "application/msword" 

I don't think MS Office file extensions are included in the default mime types known by aolserver.