Accessing variable from admin panel?

Read the codex page on creating options pages, and let us know if you run into any specific issues. It has a complete copy/paste example you can monkey with.

If you’re trying to avoid learning WordPress’ options mechanisms in favor of a more generic custom php solution, I understand where you’re coming from, but recommend learning to do it the right way. It’ll be a couple hours investment, but it’ll pay off over time. For reals.