(Not being a mac user myself, I haven't had a chance to enjoy the wonders of timbuktu but my guess is the principle bares a close similarity to other remote acess software.)
If the support pages for timbuktu aren't providing much in the way of answers maybe you could advantage of the installed VPN support of SME. This way you get past the challanges of firewall access and have all the perks of a more secure network.
Just a thought.
Regards,
Luke