So what is the best way to do this then?
Is there a way to make a particular domain, say a parked domain, that every /FirstPath run a script so I can check if it is username?

Or is there a way Unix can check in the httpd.conf file to see if the directory they entered exists, then take them there, otherwise send them to my script not just a 404.html but maintaining the directory it cannot find:

for example:
http://www.mydomain.com/foo

doesnt exists so redirect:
http://www.mydomain.com/foo/errorfile.whatever

I don't know. There has to be a way to do it to where an unlimited amount of people can access this and we not have to worry about performance. we already setup load balancing so we can add an unlimited amount of server space as the need arises, with 2 simple lines of code...

Any ideas?
thank you very much for your response.