Train T28 from Lhasa to Xining

I'd like to book 3 tickets (2 adults and one for 8 years child) soft sleeper in one cabin in train No. T28 from Lhasa to Xining on 24/08/2011. Could you please help me to arrange it? Additionally - do you help to organize Tibet Travel Permit from 20/08 to 25/08?
How much it will cost?
Thank you in advance - Regards, Waldemar