Hi Dan,
That is quite a leap in versions. If money is an issue you
may want to investigate other ways of working together.
You could 'just' work on topic content (in 2002) and then
pass this on to your colleague who can import it into X5. You would
just be adding content thougth, without adding any neat features.
Rick (the wizard) does have some tricks up his sleave with
backward compatibility, but pretty sure these tricks won't work
between 2002 and X5 - sure he will jump in if it is doable.
Good luck
Craig