SEO with dynamically created combo box

Hi guys
We have just redesigned our site, which has been created with asp.NET. The original site used plain text links which the googlebot managed to
use to a limited extent. I think the reason it could not use all of them was due to the way the url is constructed, i.e. http://www.???.com/dir.aspx?cat340. We are now using 3 combo boxes which are dynamically populated from our database. I am concerned that the googlebot will not be able to crawl using these so I wonder if anyone coould help? I had the idea of using a site map with links to all our dynamically created pages, which could be linked to each page? I would really like some help here as optimization is our life line :-)
Cheers J
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