Share SSO is broken in Labs 3.0 final/stable but NTLM works as long as you dont use SSO.
It sounds like you have NTLM working for Alfresco and the Alfresco web client.
If that is the case do the following.
if you have modified the web.xml file in the share application, restore it to its origional format.
Also, if you created the "webscript-framework-config-custom.xml" file delete it.
Users will still have to manually type a username and password, but it will be their NTLM credentials
let me know if that helps.
Adam