Rough start/idle and hissing coming from radiator

I thought I would ask this forum for friendly advice on some disappointing behavior my car developed yesterday and today. It starts out really rough, seems to be choking. Now just as I got home the engine light went on and I took a look inside and I saw this: Any ideas on what could be causing the steam? Is it radiator fluid? Is that valve an intake valve or where the water leaves the engine? Mine is a 94' 940 GL Wagon. Anyway, sorry If this is really off-base and not pertinent to normal discussions and that I'm really clueless about all this. Is this something that means I shouldn't drive my car at all now until I take it to a mechanic? Is it fine to take (i.e. drive) it to one?

looks like u need a new rad to me

get yourself a new radiator. it is an easy fix if you're a little bit handy with a spanner shouldn't take more than an hour to do

Drive but... 

You'd probably be OK to take it to your mechanic. I don't know what the engine light means. Before you go anywhere else, check and top up coolant! Is your mechanic far away? Take at least gallon of water with you and stop every 5 miles and check coolant. You could run with the pressure cap loose too just to stop the pressure building so less water leaks but keep a eye on the temperature gauge. Go slowly & don't use aircon and keep heater on full, even if it is a too warm in San Diego! You'll need to put the antifreeze mix right afterwards too. HTH Andy

Make sure the hose clip is tight and check the hose itself for splits. Looks to me though that the radiator end tank has split or the pipe that connects to the hose has split away from the end tank. Easy enough to replace, you could even have it repaired if theres any radiator specialists near you. There is the possibility that the rough running has been caused by a leaking headgasket that has pressurised the cooling system and split the radiator. Hopefully this isnt the case! Check the hose clip for tightness and the hose itself for any leaks first though. Dont let the car run low on coolant when the engine is running, this will cause serious and expensive damage.