Hi, RBC03. Turn the Powerbook off by pressing and holding the power button.
Reset the Power Manager. Try to start the machine up from your latest OS installer disc and run the Repair Disk routine in Disk Utility, in case the forced shutdown has scrambled your hard drive directory. If you can do that and DU successfully repairs anything or no repairs are needed, restart the machine normally. Let us know how it goes.
I suppose it's possible that your Powerbook has been damaged, but in most cases where the adapter's DC cord has frayed internally, then broken and sparked as yours did, the Powerbook is unharmed.
You'll need to replace your AC adapter, obviously. Apple may be willing to replace it at no cost if you explain what happened; call 1-800-SOS-APPL and ask to be connected to Customer Relations. Be patient and polite no matter what you're thinking or feeling; remember that what you're after is success, not catharsis.