Being able to register on two sites at once?

I am starting to get back in the swing of things with Boonex again.  I am going to be setting up two dating sites.  One is going to be a regular dating site and another one a christian dating site.  In order to create more users I am wondering if I could have a check box on both sites join page that could ask.  Would you like to be apart of (Whatever Site)? (check box here)

When a box is checked then I want it to create a profile on the other website as well.

Is this possible or am i going to run into big issues?

Thanks Ted

Sriptologist has a module that allows you to cross databases in admin section, therefore if someone signs up to one site, they automatically sign up on the other...

Maybe he can do a custom job for you based on this?

I love it.  I have worked with him in the passed projects.

Thanks for the advice! - Ted