For integration with a WordPress site you should first install the Page Links To plugin which will enable you to make a navigation menu link to an external site. Just create a new page within your WordPress site without any content. Scroll to the bottom of the page and select the option to "A custom URL", adding your custom URL provided by theimagefile (Control Panel > My Web Site > Naming and Access). Once that is completed you should link your Navigation Item (for example "Client Area") to your default URL (Control Panel > My Web Site > Naming and Access) on theimagefile. Your client area will now directly feed from theimagefile.
Now you should make your site on theimagefile look the same as your WordPress site to give the visitor a smooth, consistent transition from one area to the other. For best results use the Copying the layout of your external site tool. If you are unable to do this a step by step approach will give a second-best result. To start off Upload your logo, then Editing the Colours and Backgrounds page, then edit Your web site navigation menu and finally The Site Footer.
Your site is now integrated with theimagefile.