Hi,

Recently there was a need in my org to create bunch of Portal users, and I hate doing repitative things, off course I come from developing background. So I called SF premier support, asking the same, and they told I cannot create Portal Users via DL. 

I will have to create contact, hit allow login, enter user details, blah blah.. for each and every user. Did not make sense to me and I started to look into the Data Structure to see how User, Contact, Porfile, license objects are related. To my surprise there was contactId field under user object. 

All I did was populated the PortalUser.csv file with correct SF contactId, ProfileId(Partner Profile), RecordTypeId(Portal Contact) along with other info like Name, Email, Alias for 200 odd records. Uploaded via Data Loader and boom it all went in. 

I thought I will post here, so others can take advantage of this. Just shoot me an email or reply to this post, if you need further assitance.