Are you using an extra to import the posts? I suspect that it looks for a user with the same username when importing and uses the admin if that user is not found. If that's the case, you'd have to create all the users (with the same usernames) before doing the import.
It's also possible that the extra doesn't check at all and just leaves the createdby field blank, in which case, MODX would probably use the current user by default. If that's what's happening, the code of the extra would have to be modified, but the users would still have to be created in MODX before doing the import.
The Batcher extra will let you change the author of multiple resources, but again, you'll have to create the users first.
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PLEASE, PLEASE specify the version of MODX you are using.
MODX info for everyone:
http://bobsguides.com/modx.html
[ed. note: BobRay last edited this post 14 years, 4 months ago.]