The first thing I would try is checking to see of the valve on the heater core inlet is opening. I've never looked under the hood of a 98 but every other car I've looked at has one. It's usually a cable actuated valve (like a plumbing ball valve) that's got a triangle shaped bell-crank on top. The cable goes from the lever, through the firewall and connects to the heater knob (usually). Turn the knob and it turns the valve. Some of the newer cars are controlled with vacuum but I don't think Honda does. Turn the knob and make sure the valve lever is moving. It could be dissconnected, stuck or clogged. Usually easy to remove and replace or clean. Also, you didn't mention if your heater/ac fan is working. That is something else to check. Some vehicles have big resistors connected to the blower to allow for different speeds. If one has failed the you may be missing one or more speeds on your blower. So the heat may be working but the blower is not moving the hot air into the cabin.
It's not likely but it is possible to have a massive air bubble in your cooling system. This would decrease heat transfer. There should be a bleed screw on one of your large hose fittings. It should be the highest point of the cooling system. The principle being that the air rises to the top and you loosen the screw to let it out.
I would not suspect the water pump if the engine is not overheating.
If none of the above leads you to a solution then I would try disconnecting both hoses to the heater core (from under the hood) ( if you have room) and connecting a garden hose. If you can push water through the core than your problem is elsewhere. If nothing else, it's a good time to flush it. I'd flush it both way but others might disagree. Some say it causes more problems because it could dislodge mineral deposits if you flush INTO the OUT port. If you save your coolant when you drain the radiator (before you flush), strain it through an old T-shirt. If you get a lot of particulates the you may have a clog.
I hope this help you find a solution and I hope turns out easy. I know I hate working on cooling systems in the winter.

Good luck
dan :10q: