Some adapters don't automatically appear in the list of available adapters.
If you're using 2006, go into the Admin Console and manually add the adapter by
clicking on ‘Platform Settings -> Adapters -> New -> Adapter’
in the Admin Console (I have an entry on my blog that details how to acheive this with the TwoConnect Salesforce.com adapter – the procedure is the same – http://www.modhul.com/2007/02/12/using-the-twoconnect-salesforcecom-adapter/)
Cheers, Nick.