Please find the below article for how to insert users via data loader in salesforce. https://help.salesforce.com/HTViewSolution?id=000007571
Please find the below for how to insert multi-select picklists through data loader:
For inserting or updating multi-select pick list fields via the APEX Data Loader, multiple values for the field are separated by a semi-colon (;).
For example, for a multi-select field "Names", containing the values James Cotton and Otis Span, the .csv spreadsheet column for inserting the data would be entered as James Cotton;Otis Span.
Please find the below article for how to insert users via data loader in salesforce.
https://help.salesforce.com/HTViewSolution?id=000007571
Please find the below for how to insert multi-select picklists through data loader:
For inserting or updating multi-select pick list fields via the APEX Data Loader, multiple values for the field are separated by a semi-colon (;).
For example, for a multi-select field "Names", containing the values James Cotton and Otis Span, the .csv spreadsheet column for inserting the data would be entered as James Cotton;Otis Span.
Please mark this post as solved if it helps.
Best Regards,
Nagendra.P