Use below commands to restore sharepoint site using stsadm command.
Here I assume that backup file is stored in D drive with name backup.dat
1) CD C:\Program Files\Common Files\Microsoft Shared\web server extensions\12\BIN
2) stsadm.exe -o restore -url http://your site path here -filename D:\backup.dat -overwrite
After restore go to Central Administration page. In that click Application management menu. After that click Site collection Administrators which is under Sharepoint site management.
After that In primary site collection Administrator and secondary site collection administrator, you have to add the server administrator Id.