With XMP now widely supported on Windows, Adobe and other products, importing XMP tags into ZP seems very attractive. I've invested a great deal of time attaching tags to 1000's of photos and would like to know: Is there a way to import these tags?

Apparently XMP support is pending ... maybe for version 2?
http://www.zenphoto.org/trac/ticket/351

If you used Adobe to attach the tags you are in luck since Adobe has not abandoned IPTC standards. It will alias the info back to the IPTC.

A caution on reading the tickets. Unless there is an owner assigned and accepted for a ticket there is no commitment to provide the feature. In the case of XMP, there seem two issues. First, no one has indicated an interest in implementing it. Second it appears it may not be compatible with the graphics library that Zenphoto uses.