Postgres 8.3.3, GSSAPI, and Windows XP

Hello,

I'm trying to offer a Windows XP client for Postgres 8.3.3 to my
users. I have it built and installed and everything is working except
for GSSAPI. I'm getting the following error:

C:\temp>S:\postgresql-8.3.3\bin\psql -h mitchell -p 5432 postgres
psql: SSPI continuation error: No credentials are available in the
security package
(8009030e)

But authenticating against a server using krb5 authentication works
perfectly fine.
C:\temp>S:\postgresql-8.3.3\bin\psql -h vero -p 5432 postgres
Welcome to psql 8.3.3, the PostgreSQL interactive terminal.
...

Which is promising, but I'm really looking to go to GSSAPI since
native krb5 is deprecated.

I made sure that a copy of gssapi32.dll is in the same directory as
psql, and it's still giving me the same errors. Any ideas what is
going on or what I can do to fix it?

Gritty details:
PostgreSQL 8.3.3
Windows XP SP2 (32-bit)
Kerberos for Windows 3.2.2
Server is running on Red Hat Enterprise Linux 5.2, Kerberos 1.6.2

Thanks much,
Peter