How to automount SMB share in OS X
I ran across this today which is one way to do it.

In summary for Mountain Lion:


Edit the file /etc/auto_master
Within add /- auto_smb
Create /etc/auto_smb
Within add /Volumes/mount_point -fstype=smbfs,soft ://user:pass@smbserver/share


The author goes onto mention a second method using the vifs command, but I've never tried that one and it seems to do something of a pre-mount at bootup. You still have to touch the Volume for it to completely mount.

Lastly, the author states that "soft" should be used in step 4 above because failures to mount will cause the bootup to hang.