i take it its a vauxhall combi but you dont say what year/model. if its a new shape say 51 onwards they are a pain in the arse, its down the back of the engine but to remove it you need to undo the gear links to get it out, i think one of the bolts is hidden behing a rubber gromit on the bell housing. if its the early one again its down the back but dead easy to get out. dont forget to remove the earth lead off the battery first and make sure you have your radio code(you will need it when you reconect your battery)
ray
March 2009