Oh how can I bend regex to do my bidding!? (Pretty Simple)

[FuzzyLogik]

All I want to do is catch pretty much everything...

basically, I want people to be able to put the following into the address bar, and land on the same page:

mysite.com/this_is_an_example
mysite.com/this is an example

so basically I want to replace spaces with underscores (as it ultimately redirects to:
mysite.com/index.php?page=this_is_an_example3

The other problem is allowing numbers in the string, so this would work as well:

mysite.com/catch 22
(page=catch_22)
or

mysite.com/l33t
(page=l33t)

I suck as the regexp :'(

Can anyone teach me?

thanks.

[HuggieBear]

OK, first of all you're going to need to setup your webserver to serve a custom php file instead of a default 404 message.  Have you done this or can you do this?

Regards
Huggie