Lhasa via train from Qinghai/Gansu

Hey I hope someone could help me here!

I'm planning to head over to Lhasa overland from Beijing early July. I would like to take the train to Qinghai to visit some Tibetan friends for a few days, then grab the train from Lanzhou, Xining or Golmud into Lhasa.

What I'd like to know is, how easy is it to organise train tickets and Tibetan travel permits from these three cities? I'd probably not be able to organise anything from Beijing. I've heard that travel restrictions have tightened up due to the political stunt of a month or so ago - what's the travel permit situation like in Qinghai and Gansu? Sorry for asking an old question.

I've booked a plane OUT of Lhasa for the end of July... Should I perhaps aim for Lhasa via another city like Chengdu (missing out on seeing friends) or just cancel the plane while I can still get my money back and wander around Qinghai and Sichuan instead? Or is this too extreme - is the initial plan feasible? My Tibetan friends may possibly be able to help me out, but I'd prefer not to get them in any trouble. I speak good Chinese and have travelled through China before which should help.

Thanks I'd really appreciate any advice:)