Yeah, that cookiedomain is something left over from older versions - login should work fine without it.
I saw your post on the mailing list, too. Did you try the other things Tony suggested?
The two typical login problems are
1) You have $_CONF['site_url'] = 'http://www.yourdomain.com'; but try to log in at yourdomain.com (without the "www"
. Please chose one of the two and use it all the time (in the site_url variable and for logging in).
2) Cookie settings in the browser. Cookies must be activated and especially in Internet Explorer 6, you need to lower your security settings a bit before it will accept the cookie.
Hope that helps.