Question on Trusts with Windows 2003 and Windows 2000

I have a Windows 2003 network in NATIVE Mode.
I need to give access to a Windows 2000 Network that is not part of our
network or forrest.
I need to also have access to this Windows 2000 Network.

Since we are in Native Mode and the other network is only Windows 2000, I
assume we can not use Sites and Services. If I am wrong, please let me
know.

I assume we need to create a two-way trust between domains. If so, do I
need to create an 'External' Trust or can I do a 'Forest' Trust?

What we have done so far.
We entered the other sites DNS Sever as a forwarder for each domain.
We entered the other sites domain.local into Domain and Trust for the
UPS suffix.
We can ping each others domain from each site.

Any help or comments is always appreciated.

Thank You