installing xml2 for pg 8.1 on winxp

I hope I am reporting this in the right forum, if not please tell me so
and next time I'll be better.

There might be a problem with a missing extension in the pre-compiled
windows version of Postgres 8.1
It looks as though it's the 'MemoryContextSwitchTo' library which is
present in 8.0 but missing from 8.1.

I was trying to install the xml2 library to Postgres as I found it on
http://www.throwingbeans.org/postgresql_and_xml_updated.html but I had
no luck.

So I contacted Tom Dyson the author of the package and he informed me
that there were others having a similar problem with the 8.1 compile
while the library worked fine in the 8.0.3 version and he suggested that
based on e-mails he got the problem might be the one I mentioned above.

I just offered to report this problem of the build, unfortunately I
can't help much more as this is far too high level for me.

The actual error I get is:

When I run

CREATE OR REPLACE FUNCTION xml_valid(text) RETURNS bool AS
'libpgxml' LANGUAGE 'c' WITH (isStrict);

I got the error message
ERROR: could not load library "C:/Program
Files/PostgreSQL/8.1/lib/libpgxml.dll": The specified procedure could
not be found.

Thanks for the help.
Balázs