If I payed for a Flash website but my coder refuses to give me the SOURCE files, can I legally decompile them?

When you hire someone to create something for you, the "intellectual property" notion may not apply if it is a "work for hire." That is, you hired him to create something for you, so whatever he creates belongs to you, not him. He cannot claim rights to a work for hire--it's yours. However, if you have a signed contract with him, you may have agreed to surrender your rights or failed to characterize it as a work for hire. If that's the case, you may have a higher legal hurdle to get over.