Go to windows explorer and navigate to the below given path:
C:\Documents and Settings\Administrator\Application Data\Microsoft\Signatures
Place signature files in the above mentioned folder.
And make sure the signature files got copied properly at above mentioned path
Now open outlook 2007, go to …
Tools > options > mail format > signatures
You will be able see the signature in list, now all you have to so is just choose your account and set the signature as default.
Now every time you compose email, your signature will automatically appear in email.