Disclaimer The opinions expressed herein are my own personal opinions and do not represent my employer's view in anyway.
I've gotten some Office SharePoint Server 2007 questions like "why aren't slide libraries available on my site" and "where is Excel services?" They probably aren't enabled. There are two easy places to enable site features: Site Settings and Central Administration.
First, check Site Actions > Site Settings > Site Features, which will list the available features within a specific site and whether they are enabled:
If you want to enable features for all exisitng sites in the farm, go to Central Administration > Operations > Enable Features on existing sites: