You can sometimes. For example you can access Google directly by going to
Google (<--- that is an IP address, but this website automatically changes it to say 'Google').
However a web server can host more than one website at an IP address. Therefore quite often an IP address alone isn't enough to tell the server what domain you're trying to visit at that IP address/port. I'm not a computer techie, however unless I'm mistaken Eight Forums for example has 12 other domains listed at the same IP address, but when you type the actual name into your address bar it will know what site you're requesting at that IP address because in the HTTP 'Get' request it will have 'Host:
www.eightforums.com'
PS: In your example,
http://434.76.936.665 could never work because IP4 addresses can only go up to 255.255.255.255.