With some of the security changes in Vista you can no longer release/renew IP addresses or flushdns with a normal user account even if that account is within the administrator’s group.  When you attempt this with any user except for the “administrator” user you get the message: “The requested operation requires elevation” 

To get around this issue launch cmd.exe by right clicking on the icon and select “Run as administrator”.  The cmd.exe process that launches will now have the correct permissions to run ipconfig as well as other system protected commands.