I've traveled by train to the Beau Rivage Palace, which is across the street from Chateau d'Ouchy. It's a two step process, involving a transfer from SBB to Lausanne metro. The hotel is very close to the metro station, but the transfer at the main Gare is a bit of a hassle. I wouldn't recommend this with multiple or really large bags. You could take a taxi from the Gare de Lausanne, but since this is Switzerland it will cost something like 15 Fr. for a 5 minute ride. I'd imagine taxi from GVA is going to be pretty expensive.