Without knowing anything about the size of your database, the length of time allowed for a maintenance window to perform the migration, and the types of applications supported by your database, it is very difficult for me to provide advice on the best way to migrate from Oracle8i to 10gR2. I can, however, point you toward some good Oracle documentation to help you decide how best to migrate your database.
The Oracle Database 10g Release 2 (10.2) Upgrade Guide provides some very good information on the various options in which to migrate a database to 10gR2. Because you will need to install 10gR2, I would also recommend reading the Oracle Database 10g Release 2 (10.2) Installation Guide for AIX 5L Based Systems (64-Bit).
As well, the Oracle Database 10g Release 2 (10.2) Release Notes for AIX 5L Based Systems (64-Bit) is recommended reading prior to installing 10gR2.
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