Hi,
My suggestion is not to worry about a DB2 9.7 upgrade - rather perform a migration.
i.e.
you can perform the OS migration and DB migration in one step if you use System Copy (R3load)
From there you upgrade 3.5 to 7.3 (This is going to be the more difficult task)
I don't think there is a direct upgrade path.
http://scn.sap.com/docs/DOC-12042
You'll need to search the SDN for more help on the this ...
Similar threads:
http://scn.sap.com/thread/3356296
http://scn.sap.com/thread/2088669
What also seems important is whether you have SEM/Finbasis installed - this may also prohibit you from doing a direct upgrade ...
Regards,
Chris