Thanks, tigertiger, although it doesn't sound very encouraging!
I actually took a course in Chengdu 2 years ago (at 西南财经大学) and was very pleased both with the quality of teaching and the accommodation, but it was 1 to 1. The problem with 1 to 1 for me is that if you get friendly with your teacher you end up speaking English with her and then you can forget about learning Chinese for real. It's my fault rather than hers, but our last two weeks were mainly socializing. But in a group you can't monopolize the class:-)
I'll check out the featured language schools.

大家好,
I am coming to Kunming this summer and I'm looking for a short term summer Chinese course from mid-July to mid-August.
I've spent weeks corresponding with CUCAS and different universities (sent about 15 emails, got 4 replies) only to find out that (contrary to what they said in the beginning) there will probably be no group classes anywhere in Yunnan this summer, that there is no campus accommodation and that the only thing that could be arranged for me is 1 to 1 classes.
I learn better in groups and would rather take group classes in a language school, but if I have no other option I'll go for 1 to 1.
Does anyone know if by any chance there is a university with group classes and/or campus accomodation during the summer (5 weeks)? If not, can you recommend a decent language school (no self-adverstising please)?
谢谢你们