There definitely is. In fact, there are two such tools for mass importing users into Active Directory -- CSVDE and LDIFDE. The first tool (Comma Separated Value Data Exchange) is built into Windows 2000/2003/XP and allows you to import and export user accounts in a comma-separated value format. The one downside to using bulk imports in this fashion is that you cannot import passwords; this is by design. What you can do is change the domain policy to temporarily allow blank passwords, run the import, and then change the policy back. This will force users to change their passwords once they log on again.
The other tool is LDIFDE (Lightweight Data Interchange Format, Data Exchange), which is more powerful and can be used to copy passwords, albeit in an encrypted format. A good site for resources on both these commands can be found here: http://computerperformance.co.uk/Logon/Logon_CSVDE_Home.htm.
This was first published in March 2004