Wiping your HD and re-installing everything?
As the fellow above stated, if there's any data on your HDD, it must be back upped before doing anything else.
Did you upgrade to Leopard? If so take the Leopard installation disk and insert it. Then select the restart icon. When your MacBook restarts, you'll be able to reinstall the operating system.
When you're asked how you what to install, choose the option to erase and install.
When that's done you have a brand new copy of your operating system. Then reinstall all your programs. Then Apple software update will tell you there are software updates for your MacBook. Select to have all of them to be installed. Then you can copy back your data files.
If you didn't upgrade to Leopard, why didn't you?
You'll need to do the above by inserting your MacBooks' original installation disk.
But seriously this is a perfect time to switch to Leopard. Whenever Apple releases a new version of OS X, I go through this same procedure.