URI for Community: www.mycommunity.net/membername

[eluser]joytopia[/eluser]
Hello CI-friends,

I am new with CI and I would like to build a community site.

To get the site from a member, the website-visitor should type a URI like this:

www.mycommunity.net/membername

perhaps with aditional parameters:

www.mycommunity.net/membername/param1/param2

My idea was to bend the error-message 404 to a certain controller, which searches in the usertable, if a user exists or not.

Does this make sense and how can I do this?
Any better idea?

Thanks for your help!
Bernd