In reply to balmybaldwin:
I got my bits from towsure.
The mechanical stuff was easy because the holes were in the chassis with some tape over them, so no drilling.
I have a 2004 Altea with modern multiplex electronics so I bought a tronic unit (controls the lights). Despite the local dealership advising me that I'd damage the electronics and that I should pay them £850 pounds to do the job, I went ahead and spent £250, that was in 2007. I've had no problems with it thus far.
My background is mechanical, I'm an aircraft maintenance tech.
I think the main worry is the electronics, you need some form of isolation due to the way the modern electronics in cars work.
Good luck.