Import Users from D6 to D7 without directly accessing database
Views data export module is perfectly capable of exporting your users to CSV file. You would use Views to define what you want to have exported, so you can export anything. You can also use Views GUI to define mappings, if you want. It is a powerful toolset, and VDO uses all that power.

When you will have your users in CSV, you can use User Import to import them. Pretty obvious, isn't it? For mapping, User Import can


  
  Match CSV columns to account and profile fields
  


So if you didn't manage to do it on the Views level, you can always edit CSV when you'll have it locally, or try to do it on import... So many options, I'm sure at least one will work.

Last but not least, make sure your users will get mails with "new password required" explanation, as D6 and D7 stores passwords in incompatible ways.