Create self signed x.509 certificate with signature algorithm sha1RSA

I am using BizTalk 2009 to trade XML files over AS2. I am trying to
create a self signed x.509 certificate with signature algorithm
sha1RSA using certreq.exe on a Windows 2008 server. I cannot get the
signing algorithm to be anything other than RSA.

Anybody create their own x.509 signing certificate for sha1RSA?

Thanks,
Mike