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Your reason for poor positioning in Google probably has nothing to do with xoops, or queries in the URLs or meta tag content. Google has no problems crawling XOOPS URLs and takes most of its index data from actual page content, rather than meta tags.
Other search engines DO rely on meta tags AND have problems crawling URLs with query strings, so that may be worth considering in terms of using XBS and simplified URLs hack
Google places XOOPS sites very high in page rankings and search results. I can attest to this on my own sites and many others here will agree with this. Sure there are improvements we could do to improve ratings, but first and foremost, you need lots of relevant content and I mean 100s or 1000s of pages all having your keywords/phrases high up in the pages.
Then as many incoming links from high PR sites as possible which are releavant to your own content.
Daily input also helps a lot, as site with changing content is recognised as 'newsworthy' Google is more likely to crawl frequently with regular changing content.
It's all been written here before, so do some digging as suggested above.