You reset the ECU (on my '98) by pulling the backup fuse out (#13 in the fusebox in the passenger end of the dashboard). Leave the fuse out for something like 20 or 30 seconds. That'll clear check-engine-light codes, but I DON'T think it's going to fix your fuel warning lamp.

I think the fuel sender (in the tank) has a contact that closes when it's near empty. So one of the wires to the sender is there to turn on that lamp. If the contact is messed up, or that wire is shorted to ground, it'll light up all the time.

I'll have to try to remember to look for that in my Helm book. But I'm not really sure if it's the same for your 2000. You'd be a lot safer by getting your hands on a Helm manual for your car.