John
Just to clear that up : the reason why it is register.aspx is because the Url Master module drops the /default.aspx whenever it isn't needed (which is most of the time). The Url is home/ctl/register.aspx , which is rewritten to default.aspx&tabid=xx&ctl=register - the standard Url for the register control. The Url Master module just puts all the register links back to the home page to eliminate duplicate register Urls for each page.
Not sure if your method of a custom registration will work because I think the ASPDNSF registration control can't be placed onto any old page : i'm pretty sure it only appears when you request ctl=register on a page (again, could be wrong, happy to be told otherwise).
My guess is (and I've never seen the code) but the aspdnsf register control (which gets you to repeat your name address and puts in the 'over 13' checkbox etc) is probalby looking for an upper case 'R' when inspecting the query string. As I said, it's just a guess, maybe one of the aspdnsf developers could let us know.
As for the 404 errors on the categories, that is a PEBKAC error : Problem Existing Between Keyboard And Chair. The keyboard being the one in front of me, and the chair being the one holding me up off the floor. I am the guilty party who broke Cliff's site with an incorrect configuration. It's fixed now, and you can add a public apology to Cliff along with the private one already sent.
-Bruce