Presumably you're referring to categories and/or ads? WordPress has built in Import/Export tools, so if you're importing from another WordPress blog you can use this, otherwise you would have to look at plugin options for importing a file such as XML format.. Both of these methods should work in terms of initially moving them to a ClassiPress site, but you will need some knowledge of sql to migrate the categories/ads into the correct location i.e. "Posts" to "Ads".. and the fastest way is to do this is to create a custom sql query.
