<p>Can anyone recommend some good resources that highlight the differences between Oracle and the AS/400 database?</p>

<p>I am trying to help someone with a lot of AS/400 experience implement an Oracle installation, and they need some guidance.</p>

<p>A book or online resource would be ideal.</p>

I've done this a fair few times and the solutions out there really depend on the environment (enterprise / mission critical or development).  The BEST way would be the
Oracle AS/400 Gateway
.  Here are some important links in that area:
Allow AS/400 apps to access oracle with the Oracle Access Manager:
Installation Guide for the AS/400 Oracle Access Manager
Allow your Oracle apps to access AS/400 tables and be queried using Oracle:
Oracle Transparent Gateway for DB/2
^^^Those products are fairly expensive but super powerful.^^^
Alternately, here are some more academic approaches to the situation:
Here's a technical comparison of the two technologies... It's a little propagandaish*.
Technical comparisons of Oracle and DB/2
Here's a document written from the opposite point of view - Someone moving from Oracle to DB2.  I still find it's useful information:
Leverage your Oracle 10g skills to learn DB2...
And another IBM link that has some really great information all around:
IBM Developer Network Search Results
Hope this helps!
*Yes, I know propagandaish is not a real word.