upgrade to 8.2.? or implement Slony, which first?

We plan to upgrade from our current 7.4.17 Postgresql to 8.2.? in the
near future.  We also plan to implement a replication solution, most
likely Slony.

We know that the upgrade to 8.2.? will require some code changes.

Question is, is there a particular order in which we should perform
these changes that would require the least amount of additional work?

That is, would it be more efficient to move to 8.2.? and then implement
our Slony replication, or would there be less effort in implementing the
Slony solution and then upgrading to 8.2.? ?

--
Until later, Geoffrey

Those who would give up essential Liberty, to purchase a little
temporary Safety, deserve neither Liberty nor Safety.
  - Benjamin Franklin