User profile migration from local profile to domain profile

Hi All,
Im helping my customers to create a domain for the to do Single Sign On for MOSS Server that we implement. At first Profile Migration is not inside our scope, but then it got included, which give me little time to prepare.

Ive tried using the copy and paste method, and according to my little experience, this works when migrating domain in my previous company, But somehow i keep getting permission error on the client PCs that i used in the Clients office. although i already added the permission, this error keep pop up.

i already tried USMT, but cant seem to get the command rite, and loadstate doest seem to export the PST, which is 1 of their main requirement. they cant be manually transfering pst file for almost 300 PCs.

so i tried another method, which uses the built in profile copy. I go to My Computer, Properties, Advance, User profile and Copy To function. But during testing, 1 of the user folder is missing, and although i know this is a 1-off incident, the client refuses to use this method.

I also used Profwiz, which can migrate the profile very fast and accurate, but this method overwrite the old profile, and you cant login to the old profile anymore. My Client wants the user to still able to login to old profile in case something go wrong. so this method is also out.

because a lot of my method is rejected, they told me that they would consider payed solution, which im still searching for the best application that can do this.

any help from the community here is greatly appreciated. Maybe you all can help me with USMT, which i read is the best method. i still cant get the code to work rite.