Domain Alias, duplicate content, google death?

two domains pointing to one site=instant death?

[alxdean]

Here is my dilemma.
I have a client hosting with me who decided to change the name of his company. That is after he sent out thousands of catalogues to his clients telling them to go the website to place an order.
Being ****scared of duplicate content on google I changed the original site to include a robots.txt on www.xyzcompanyLtd.com, disalowwing all robots all content.
and placed a copy without the robots.txt on the new site www.Myxyzcompany.com.
But this can not work in the long run. I'm talking about hundreds of web pages, thousands of products. I can't be updating both sites the whole time. It also creates a management chaos regarding email addresses, email forwarders etc. etc.

So here is the question:
Can I set up the old domain to be an alias of the new domain, effectively pointing to the same IP address without being banned from google?

301 redirects are not an option
I could use a global.asa to redirect any session request but am not sure of the effects on google and don't want to fall under the doorway page category.
Putting a "this site has moved" page up is not an option either.

I need to have a fully functioning copy of the website under the new domain and old domain. The user experience must not be hindered through annoying messages or sudden redirects.
The best option would be to alias the new domain on the old domain name. but I am scared. really scared.

any help appreciated.

Alx

[alxdean]

WOW, talk about two people having the same thought.
recent post :http://www.webmasterworld.com/forum3/10006.htm
is talking about pretty much the same issue, posted while I was phrasing mine.
Will repost my question in his post.