Thanks for the helpful comments.
After spending a day experimenting, my current thinking is to use new Linux but keep PostgreSQL 8.4 (for now at least), and update only what is necessary in our code to work with NaviServer. Then look at incorporating more OpenACS updates and new db versions as a longer term project.
Looking at the documentation, I think the ns_cache_transaction features of NaviServer could be very useful - I've always found it annoying that when a transaction is aborted the cache is left in a potentially wrong state!
Cheers
Joe
