Andrew has posted some useful links for Tibet on his blog.  Here they are

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Tibet Links

Here are some links to information on traveling in Tibet:

 

Legal / Health Information

Passports / Visas

http://www.china-embassy.org/eng/hzqz/zgqz/t84246.htm

 

US Department of State Travel Advisory for China

http://travel.state.gov/travel/cis_pa_tw/cis/cis_1089.html

 

CDC (Center for Disease Control and Prevention) - Health Advisory for China

http://www.cdc.gov/travel/eastasia.htm

 

Fun Information

Tibet Travel Faq / Travelogue

http://www.travel-library.com/asia/tibet/tibet-travel-faq.html