Can I move 600+ users from a standalone server to a PDC with all rights and information intact, without having to recreate the users on the PDC?
Well, there might be an easier way with a third-party utility, but you can partially accomplish your purpose with a couple of utilities from the NT Resource Kit.
First, you can use the AddUsers.exe with the /d syntax to dump the current user list to a file. Then, you can use AddUsers with the /c syntax to create those groups and users on the PDC. You can even edit the file created before adding the users (the Resource Kit gives you an example of the file structure).
Now you have the users and groups, but not the security. Hopefully, most of your security is based on having each user assigned to one or more of a relatively small number of groups. If so, you can set up the security for those groups (which were copied with AddUsers), then assign the users to the group with the UsrToGroup utility from the RK, which uses a text file to accomplish it's purposes.
For specific rights, you can use the SubInACL utility to obtain security information on files, registry keys, and services, and transfer this info from user to user, group to group, and domain to domain.
It isn't a one-step process, but it's certainly easier than doing it all by hand.