For Windows Vista/7 you can avoid request of admin privileges by using Default Programs (http://msdn.microsoft.com/en-us/library/cc144154(v=VS.85).aspx). Just add some registry keys during installation. Example:
Windows Registry Editor Version 5.00
[HKEY_LOCAL_MACHINE\SOFTWARE\RegisteredApplications]
"DBFCommander"="SOFTWARE\\DBFCommander\\Capabilities"
[HKEY_LOCAL_MACHINE\SOFTWARE\DBFCommander]
[HKEY_LOCAL_MACHINE\SOFTWARE\DBFCommander\Capabilities]
"ApplicationDescription"="DBF Commander is the most powerful tool for DBF files viewing, editing, creating, converting and SQL queries executing!"
"ApplicationName"="DBF Commander"
[HKEY_LOCAL_MACHINE\SOFTWARE\DBFCommander\Capabilities\FileAssociations]
".dbf"="DBFCommanderFile"
".fpt"="DBFCommanderFile"