Redirecting Forwarded Domain to a Subfolder

[Johnnie Norsworthy]

I have a web site Domain1.com and a secondary domain, Domain2.com that is
forwarded by my registrar to Domain1.com.

Using my primary home page: http://domain1.com/default.aspx is there a way
I can recognize that it is actually forwarded to by Domain2 and redirect to
a subfolder of the actual site: http://domain1.com/domain2/default.aspx?

Using IE, when I type in Domain2.com and the default page appears from
Domain1, the address line in IE *does* say Domain2.com

I hope this wasn't too confusing, and I am use the way to check in my
default.aspx page will be easy, but I don't know what to check. I have no
problems with the redirection aspect, just recognizing when it should do the
redirect.

Thanks for any assistance,
-Johnnie