In reply to coldfell:
June/July 2010, we used the trains, as summarised by drolex above.
Eurostar afternoon from St Pancras to Paris Nord. Metro transfer to Paris Austerlitz.
Overnight couchette from Austerlitz to Pau, then morning local train to Oleron Ste Marie.
Bus to Etsaut, then plenty of time to walk to first hut.
Did parts of Haute Route/GR10/GR11 then returned from Luchon couchette to Austerlitz.
Everything booked easily via Dbahn (either online or phone the London office).
The only slight hassle was on Eurostar, we had to hand over our axes etc at St Pancras and retrieve them at Paris Nord. There were 4 of us so we just handed them all over in a single rucksack liner.