UUID generation functions

Sorry for the OT post, but does anyone know if there are any internal
UUID generation functions in pg?  I took a quick look at the 8.2 docs
and didn't find anything related.

I know I can spawn a call to the underlying system to get a UUID.  The
problem is that calling out to the system for this tends to lock one
into a specific O/S.  In the case of Linux, uuidgen is _usually_
available for this; on Windows, however, a custom app to call a specific
API would be necessary.

The idea I had was to call this internal UUID generation function in an
INSERT trigger to generate a unique, traceable that identifies a sample
as it traverses numerous information systems/databases.

Thanks in advance,

Gord Hyatt