Categories within the software once created have a "stable" url that you can link to from anywhere around the Internet. Links to categories within the software need to take a specific form and contain the category id for the category you wish to link to. You can link relatively within your site by creating a link like the one below. If you have "index.php" as base file name within your site that link would look like:

index.php?a=5&b=XXX

All you need do is replace the "XXX" with the category id to the category you wish to link to. That category id can be found in your admin tool by navigating the CATEGORIES > CATEGORIES SETUP admin tool. Next to each category name is the category id for that specific category. Each category id is unique.

You can link into that category from anywhere on the Internet by using the full url. If your site happened to be "mysite.com" the link to a specific category would look like:

http://www.mysite.com/index.php?a=5&b=XXX

where "XXX" is the category id to the category linked to. The above links should work whether you have the SEO addon turned on or not. If you do use the SEO addon you can use the "rewritten" url if you wish but you will need to obtain that link by linking into that category on the client side and copying the url you see in the address bar of the browser after linking in.