Hi,
I've configured JIRA on
jira.xwiki.org to display the description field and
the comments using the wiki rendering feature. See
http://www.atlassian.com/software/jira/docs/latest/renderers_overview.html
for details.
In short, here are a few interesting macros:
{code} : display code
{noformat}: displays unformatted text (for example
http://jira.xwiki.org/jira/browse/XWIKI-595)
Let me know if you have some issue with this.
Thanks
-Vincent