I was going to suggest Brutus-AE2 if you are stuck with using a Windows Box. But then I noticed with some small degree of sadness that it's no longer available as the site that hosted it Hoobie(dot)net is gone. *sniff* it will be nostalgically missed.

THC-Hydra has been much revamped of late and version 6.1 is available and it compiles cleanly under *nix, but sadly also no longer available for Windows as indicated by the change log and the words "Not Anymore!" 

The only other parallel network login brute-forcer on Windows that I could find is:

Bruter 1.1
Bruter is a parallel network login brute-forcer on Win32. This tool is intended to demonstrate the importance of choosing strong passwords. The goal of Bruter is to support a variety of services that allow remote authentication.
Available at: http://sourceforge.net/projects/worawita/