How can I best set up an smtp queuing system on either OS X server
10.4 or windows sbs 2003 in order to queue mail destined for a mail
server at another location that has an intermittent connection?

One) Intermittent connection?  Up For an hour everyday around noon or 
something totallly random.

Two) How much mail do you expect? 1 user? 100 users? BIG files or smal?

The destination mail server's connection would be up almost
permanently but may occasionally drop for an hour or maybe a day as
happened recently. It could be handling mail for anything up to 50
users... maybe some big stuff too so I'd need a robust solution.

Any SMTP server will hold mail for a configurable number of
retries/time if the remote server can't be reached.

I'd think you could accomplish this with Postfix, tweaking the backoff
timers so that the delay between retries was more suitable for your
situation. Maybe put something like this in main.cf:
 
queue_run_delay = 180
minimal_backoff_time = 300
maximal_backoff_time = 3600
maximal_queue_lifetime = 259200

That would make postfix retry the SMTP connection no more than once
every 5 minutes (300 seconds), but no less than every hour. It would
also give messages 3 days before expriring as undeliverable should the
connection not complete in that time.