D20 3.5 Post-Apocalyptic Campaign?

[aphoticConniver]

I'm trying to run a real-world 3.5 campaign (meaning no magic) that will be heavily exploration-based. Has anyone made classes for such a thing? Are there rules for what few guns there may be? Are there any inherent flaws in the idea? What the party will be fighting is of the supernatural and possibly extra-dimensional persuasion.

[malonkey1]

You're gonna want D20 Modern (http://www.systemreferencedocuments.org/resources/systems/pennpaper/modern/smack/srdhome.html).