vacuum process stuck

I was attempting to clean up one of my databases and so I ran 'vacuum full' on
the database. However, after at least an hour, it seemed stuck, so in the
terminal window I hit CTR-C to cancel out of it, but it still hasn't quit (it
said the following:

# vacuum full;
^CCancel request sent
^CCancel request sent
^CCancel request sent

When I run top, it says this process status is in 'biord', which according to
the FreeBSD lists corresponds to buffers being read or written. So, how long
should I wait for this process to finish? I know one of the tables in the db
probably has ~20-30 million entries in it.

Any suggestions? I assume I absolutely should not kill the postgresql process
that is running the request, so what are some other options?

TIA.

-doug

details - FBSD 4.8, postgres 7.3.2_1