In WSS3.0 and MOSS2007 the validation available in columns was limited.
CodePlex projects are available with custom field types to help here. Obviously this is limiting if you want to expose these columns in the Document Information Panels (DIP) in Office applications.
In SPF2010 and SPS2010 there is limited validation, in that you can specify one validation rule for a single column. Unfortunately Regular Expression validation is still not available out of the box.
External References