Hey guys, thank you a lot for your help.
Finaly I used this combination :
a powershell script launches a .bat file in admin mode :
Start-Process C:\filelocation.bat -Verb RunAs
Then the .bat makes some copies (robocopy) and at the end launches TestExecute with admin privileges as it has been set with the ps1 script
And at the end, I don't use the "net use" command but the build-in TestComplete commands :
aqFileSystem.DisconnectNetworkDrive('n:', True, False);
aqFileSystem.MapNetworkDrive('n:', '\\drivelocation',
'domain\login', 'password', False);