Can I travel to Tibet with a travel agency as usual?

Anybody who holds the common passports can go to Tibet for a visit through any of the local travel agencies, except for the following three kinds:
1. Those who holds the passports relating to embassy or ambassador or working in there
2. Government officials
3. Journalists
these three kinds of persons can take a trip to Tibet via governemt office, Foreign Affair Office, Economic Development Committe, etc. but not through the travel agency