It looks like its the turbo water pipe! Not 100% sure but that bracket in that location makes me think it is. Sorry if its not.

Brake line. Not sure but I think it goes from the proportioning valve to the master cylinder.

Is it the narrow or larger tubing? Can't tell in the picture. Also it looks like the hardline for your power steering.

Kinda long shot but looks like drivers side line from master to wheel well brake line, since it has that bracket on it.

Have not looked at mine in a while, but it looks to me like half of the turbo oil feed line from the OFH (not all of it, as that is two piece).

bing, bing, bing! Iceman510 has got it! Just looked under my 99 GST. It's the turbo oil feed pipe half from the oil filter housing (which connects to the other half going to the turbo). Here's a pic of it in place: