Hello. we are looking to upgrade our operating system on our database server (DB2 v8.2) from sles-9 to sles-10SP2. i would like to know what should be done, from the database side, before and after this upgrade. Thanks

make a full/offline backup.
Then upgrade. If it still works, fine. If not re-install DB2 and re-create/restore your database.
and ... try it on a test-server first...

OK thats fine but are there no specific configurations or settings that must be changed or updated? If yes then you're saying that I simply do a full offline backup and restore after the os upgrade?

All you need to do is to stop the instances and then upgrade the OS. Nothing should happen to your db2 installation/instances/databases, but taking an offline database backup prior to the upgrade is a good idea. During an OS upgrade, permissions on db2 binaries may get modified and as a result you won't be able to start the instance (sql1042c). If that happens, you'll need to update the instance using the db2iupdt command. When upgrading the OS, always verify that you meet the minimum DB2 requirements (ie. kernel/libraries level). For DB2 v8 and SLES 10, they're documented here:
IBM developerWorks: Wikis - Information Management - SUSE Linux Enterprise Server (SLES) 10 - DB2 UDB V8.2

Thank you kindly, db2girl and dr te z