Given an MOSS bak file which looks something like blahblah.DAT. You will need to do the following to install it on your MOSS installation.
First you will need to go to your MOSS Central Administration Page and create a site collection. For example
http://localhost/sites/test_site_collection
of you could simply go to
C:\program files\common files\microsoft\shared\web server extensions\12\bin
and type the following
STSADM.EXE -o createsite -url <url-to-site-collection> -ownerlogin domain\user -owneremail <email-address>
Next you will need to navigate to the following location using command prompt
C:\program files\common files\microsoft\shared\web server extensions\12\bin
Once you are here type in the following command
explorer .
This command will open this location and you can copy your blahblah.DAT file here via copy and paste.
Next go back to your command prompt you can type in the following command
stsadmin -o restore – url http://localhost/sites/test_site_collection -filename blahblah.DAT -overwrite
Click enter when you are done.
To see the restored sitetype
iexplore http://localhost/sites/test_site_collection