Replication for migration

Hi list!

I've to do a migration of postgresql from version 8.2 to 8.3 in one
server. The problem I see here is, to avoid data loss (people still
using the web site that uses postgres), I'll need to stop postgres 8.2,
make a pg_dumpall, and then restore that information in 8.3.
Taking some considerations, like database size, server, etc. I estimate
that it will be at least 30 minutes of downtime, and that's pretty much
time.

I've thinking in the possibility of doing some kind of master/slave with
both versions (I must change the default port in one of them, as
everything must happen on a single machine), and find some useful links
like:

http://wiki.postgresql.org/wiki/Replication%2C_Clustering%
2C_and_Connection_Pooling
http://momjian.us/main/writings/pgsql/replication.pdf

I'd love to read some experiences or advices, since I haven't done it
before. Also if you have some link o document that you think I must
read, it'll be welcomed.

Thanks to all.

Martín