I take it the problem is the chart is not showing, is that right? A couple of things to check: is the content set to HTML, so escape="false". Also, is the computed field rendered to the browser. If rendered is set to false, your code will not get passed to the browser.
When working with charts I usually put the same code in a second computed field, so I can debug it. I show that field (or set the rendered property so it only shows if I want it to) and also make sure escape is NOT false (i.e. set escape="true"), so it is not written to the screen as "pass-thru HTML", as it were.
I take it you've seen the two articles on the App Dev wiki, but if not, the first one is here: http://www-10.lotus.com/ldd/ddwiki.nsf/dx/Dojox_Charting_for_XPages
There are also links to a sample database.