It's a heap overflow, wich makes it much harder to write a working exploit, due to the dynamic stack.
There's a POC (just to check for the vulnerability) at:
http://metasploit.com/tools/ms03-046.plH.D Moore is also supposed to release Framework 2.0 in the next few days, and hopefully, this framework will include a working version of the exchange exploit, as is suggested here:
http://metasploit.com/tools/msfweb.jpgCheck the metasploit projects in the next few days...(metasploit.com).
Core Impact also has a working version of this exploit.