How to make an existing windows 2008 domain a part of new company forest

We have an independent Windows 2008 domain with about 1800 user / computers. We started with windowsNT, migrated it to Windows 2000 then to 2003 and are now on 2008. We are now asked to become a part of the company domain / forest which is being established. This will perhaps require a change in my domain name too. As our windows domain computer have been a part for domain for very long a lot of things like mail clients and other application clients are tied up with the domain user profile. In such a state if the parent domain changes what will be the effect on these?  i do not hv a choice of making my domain a trusted domain of new company domain.
Pl suggest what action plan I should have to have a seamless transfer?
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Glen KnightCommented:
You cannot join an existing domain to another domain.

You would need to migrate users/computers/groups to the other domain using ADMT.

See the guide here:
Beat me to it, what above poster put.
u still need to establish an external trust between the two forests.  I wouldn't use Microsoft's ADMT tool, I would use a tool like Quest Migration Manager,
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Glen KnightCommented:
I don't believe there is a requirement for trusts to be established to use ADMT.  It works on SBS which doesn't allow trusts to be created.

Why would you pay for quest when there is a perfectly good free tool?
U are going to need a trust, the two forests need to communicate.  ADMT will not do mail.
Glen KnightCommented:
They will not need trusts to use ADMT.  ADMT will transfer the required users/groups/computers.

There has been no mention of mail but if Exchange is involved depending on which version there are ways to move mailboxes between forests.  And trusts are not required for this either.
archmukAuthor Commented:
Actually, establishing trust is not an option for me. The need is for our present domain to become a subdomain in the new forest. We cannot exist as independent domain after the company forest is established.  
So i need to know what do i need to do so that the existing user profiles on the present domain computers get migrated to new forest/domain without any corruption / loss.
Glen KnightCommented:
As I said, use ADMT.

There is no other way to achieve what you want other than 3rd party tools which are not required because ADMT will do it and it's free

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archmukAuthor Commented:
Thanks demazter for the solution. It does seem to be a long solution but it should work in my scenario. I will try the same in my test setup and update.
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