It will be kind of hard passing 223 without some Unix / AIX administration experience. (But (unfortunately) it is possible.)
This is a good place to start:
IBM: Test 223: System p Administration
Many certification programs today seem to be geared towards supporting training programs, and IBM is not too far behind in this ugly trend. (Before I get backlash, please compare the AIX 5.2 CATE requirements with those of 6.1. Then also note that there are no longer test prep (specific) RedBooks for any of the CATE required tests.)
That ranting aside, 223 was NOT a major revision from the previous version. (At least not when I took it.) And there IS a RedBook for the previous exam. It can be found here:
IBM Redbooks | IBM Certification Study Guide eServer p5 and pSeries Administration and Support for AIX 5L Version 5.3
My strong recommendation will be to get some "clutch time" on an AIX system. If you are trying to jumpstart your career with a certification, I would recommend "supplementing" that with some real experience.