Before you upgrade to Tiger, please backup your databases which should be in /Library/OpenBase/Databases/ or /Users/Shared/Databases. Make sure your databases are in a safe place. After you upgrade to Tiger, please reinstall DayLite 1.7.5 (and DMI 1.2 if you use it) and then restore or copy your databases. On a new install of DayLite v1.7.5, the default databases location is in /Users/Shared/Databases. If you've upgraded to Tiger before backing up your Databases, you should find them in /Previous System/Library/OpenBase/Databases/. 

DayLite v1.7.5 and the database engine run on Jaguar, but some OpenBase components do not (such as OpenBaseManager). If you are very dependent on Jaguar, you should not update to v1.7.5. You should remain with DayLite v1.7.3. As we move forward, it will be impossible for us to maintain compatibility with Jaguar. We urge you to upgrade to Mac OS X 10.3.9 or Mac OS X 10.4.x at your earliest convenience.

There are no schema updates, so this should a pretty simple upgrade. The database engine itself has been upgraded to OpenBase 9 OEM (#20). You must upgrade all computers using DayLite simultaneously. If you currently perform offline/online syncs, you should recreate your offline database(s), otherwise you may lose data.