I'm probably just being a bit slow on the uptake here. Do I understand that the passenger window goes up and down when it's switch is operated in the passenger door and also when the switch in the drivers door which operates the passenger window is operated. I don't know what you are meaning when you say "holding the key down" but I'm guessing you're talking about the remote? If this is what's happening then, taken that you've replaced the switch in the drivers door, my bets would be on a broken wire where the door loom transitions to the body through the flexible connector sheath. If this is the case the rubber can usually be peeled back to reveal the internal wires and you solder up and heat shrink insulate the break or patch in another bit of wire if it's all in too much of a mess. If you do an internet search there are often aftermarket loom sections available at reasonable prices (ebay etc) and these can be a good solution if several/many of the wires are damaged. The insulation cracks with age and the constant flexing due to the opening and closing of same. Hatchbacks are particularly prone to this happening where the wires transition between the hatchback and the body. It can be a nasty fiddly wee job which many garages don't like doing and can cost a good few bob, especially if you need to remove door cards etc. I don't particularly like doing it but the materials involved in a diy repair are minimal so costs can be kept very low.
