Well, all of them do this prior to the '02 models at some point. They usually crack behind the alternator but some crack at that heater hose nipple there at the rear of the intake.
You can't really bypass the heater core and drive it is the intake nipple that is at fault. Your most likely going to have to replace the complete intake manifold with the updated intake with the alum. crossover.
If your not mechanically inclined, you will need a mechanic to verify that this is whats happened here. If so, your out a car for a time.
Don't drive it to a mechanic as it will overheat again. See if he could come to it.
Do a search on this sight, there is a lot of good info on this issue here. I replaced my '98 nPI with a Dorman product and have had no issues. There are others.
Good Luck, GT
'09 Lincoln MKZ
Dk. Blue Ink Met./Lt. Bone
'98 GT Cpe./5 Spd./3.27:1 axle
Black Clearcoat/Med. Charcoal