soorma,

As a rule -- I don't t recommend modifying the core code, but I'm curious as to what you need to check for before someone can register. What business need are you trying to satisfy by modifying the registration? Maybe there is an alternate solution.

take care,

Ian

You might want to look at the DataSprings Dynamic Registration module.  If it provides the functionality that you need, thats a much safer approach than trying to modify the existing code.  On advantage is that this approach is the least likely fail when you upgrade your site to a later version of DotNetNuke.  It's also in keeping with the good architectural design of DotNetNuke.

If you MUST dig into the code, you might consider creating a special Membership Provider.  If you simply need to do some things prior to actually registering a user, the appropriate place to do it would be in the Membership Provider.  And, I'd install this as a separate provider.  There is some good information about Membership Providers in the Professional DotNetNuke book by Shaun Walker, et. al.