[Koha] Slightly odd install/upgrade request

[Nigel Titley]

Folks,

I find myself in a slightly odd position. Up until a couple of months 
ago I was running Koha 1.2.3 very satisfactorily. At that point I 
rebuilt the box it was running on and installed Ubuntu. Koha wasn't too 
high on my urgency list (getting my ecommerce site back was rather more 
urgent). However, I had taken a database dump so thought I could easily 
rebuild Koha when I had the time.

My game plan was going to be to re-install 1.2.3 from scratch, overwrite 
the database with my saved copy, and then progress up through Koha 
releases until I got to the current one.

I sat down last night to start the process and found, horror!, that koha 
1.2.3 is no longer available for download, so my game plan was scuppered.

As an experiment, I tried installing 2.2.6 with the existing database in 
place, and got a number of complaints from the installation and a 
general feeling that things hadn't gone properly.

I now know about the mysql4/5 problem, and will rewind the database 
server to mysql4 before I start again, but can someone give me an idea 
of how I should proceed? Have there been database changes between 1.2.3 
and 2.2.6? How should I get my 1.2.3 data into a new install of 2.2.6? 
Just a general hint or two would be helpful. I'm reasonably competent 
with databases, perl and  unix cli.

Help!

Nigel