Hi John, I used Saphir Voyages for a trip into the Sahara and found them very good. Their phone number is 00 216 72 240168 and I booked them by phone from the hotel. Be sure to ask for an English speaking guide - they pick you up from the hotel. Also bear in mind that public transport is very cheap in Tunisia and there is quite a lot you can do independently, though you will have to go into Sousse for the train, metro or bus stations. I think the louage (shared taxi) is also in Sousse. I'm in Denmark at present so not on my own computer but will be home this weekend so if you think I can help any more you only have to ask.