I went to Sestriere early last September. Would highly recommend it as a altitude training camp. Sestriere is in the Alps and is very close to the French border with Italy. There is an excellent running track and lots of trails very close to the town centre. The leisure centre has a good gym. Tempetature can vary quite a lot with the mist that sometimes hangs over the mountains but on the whole it will be warm and sunny in September.
There are lots of places to stay as Sestriere is a top winter ski resort.
Currently there is quite a lot of building work going on in preperation for the 2006 winter Olympics.
From Turin airport you can reach Sestriere by public transport easy enough.
Nice places to eat and a few bars as well.
This was my first experience of altitude training and I certainly noticed the benefits when returning to sea level. I stayed for three weeks and only started to get a bit fed up in the last week.