If you attempt to bid on a stallion and it continually asks for you to login, then cookies are not enabled on our browser.  Cookies are required to be enabled for this site to function.  In Internet Explorer, go to Tools\Internet Settings\Privacy and make sure that it is set to the default setting.  Close and reopen Internet Explorer and try again.  If it still does not allow you to bid, then change the Privacy setting to the lowest settings to accept all cookies.  Place your bid and then change the setting back to the default setting.