Thank you for using our services.
We do have built in Url rewriting functionality, which uses regular expressions for defining patters which are used in rewriting Urls. You can take a look at the following webinar for more information on Sitefinity Url Rewriter: URL Rewriting In Sitefinity
If you can not use regular expressions you would have to write your own HttpModule and add it to the website. The best approach here would be to inherit from the Telerik.Cms.Web.CmsHttpModule and substitute the original one in the web.config:
All the best,
the Telerik team