Re: 2000 GTP...Retros, Different stuff.
Red, yes I think they do sell modules that will do this but you'd need 2 or 3 of them since they only control 2 windows each (I'm counting the sunroof as a window). This was basically free, and it was stuff I figured out in my head as I went along.
Bandook: that'd be a combination of features really. You'd basically need to do everything I have done, plus the rain sensor stuff. What I have set up is one touch modules (which roll the window all the way down or up when each wire gets a +12v pulse), then relays to send that +12v pulse whenever they receive a ground pulse. The alarm sends out a ground pulse, which triggers a relay(since the alarm can't take the load of 4 relays) that triggers 4 other relays that trigger the one touch modules (1 in each door). That is all for 1 direction, up or down. If you want up and down, double all that. The rain sensor will also provide a negative trigger, just like the alarm, but the rain sensor and such will determine when that negative trigger is sent. Not sure if I've shown it to you or not, but I have done a write up on the one touch modules. That'd be the first step, and allow you to roll all your windows up\down with one touch of the window switch, just like how our driver side's window is on down.