Domain / Host address issue

I have my worpress site located at http://www.host.com/mywebspace/worpress

I have http://www.mydomain.com pointing to the host, so the blog posts are http://www.mydomain.com/?page_id=98

I have links within the site pointing to ?page_id=98, so they come up as http://www.mydomain.com/?page_id=98

However, for the links of lins to the blog archive (i.e. ones that wordpress link to as opposed to what I enter them) it comes up as http://www.host.com/mywebspace/worpress/?page_id=98

Any ideas how to get WP to recognise mydomain ?