if stsadm is not present in your new wss 3.0 installation, something is wrong.
it should be in Program Files\Common Files\Microsoft Shared\web server extensions\12\BIN
is this a standalone installation? if not, please explain how you did your install.
if this is a new wss 3.0 installation and it's not some kind of unique install scenario, it may be best to just uninstall and reinstall the binaries. because if stsadm is missing, who knows what else is wrong.