Not good to see these post go unanswered. The XOOPS theme overrides the WordPress (xPress) module. For the theme to show, you have to produce a XOOPS compatible WordPress theme and turn off the current XOOPS them for WordPress (xPress).

I think there is mod which can switch themes, depending on the page it is set to display. I do not think you can not do any of this with first hacking the XOOPS theme to properly allow WP's theme and template to co-exist.

Strat