You can add a login form to any category page by putting the special tag {login_form} in the content area. Also you can manually create a login form if you need to, just copy and edit the html code that is generated for the login form and put it anywhere in a page template or in content area.
If you go to Admin -> Settings -> Users you can also set a Login Redirect URL so when someone logins in they will go to that url. By default successful login brings the user to their account page.