Lets go back to the basics of IP addresses and their naming format.

An IP address is the unique identification code of a machine connected to a network (local or www)

The name eg.www.google.com is just an alias of the numeric ip addresses(here IPv4)

Try this:

1)Windows -> Run ->cmd

OR
1)Linux ->open terminal

2) ping google.com

Pinging google.com [72.14.207.99] with 32 bytes of data:

The bold part is the IP address but wait an alias might have multiple associated ip addresses

3)nslookup google.com

Non-authoritative answer:
Name:    google.com
Addresses:  64.233.167.99, 64.233.187.99, 72.14.207.99

4)www.google.com is also valid but google has different servers.

5) The addresses obtained can be used http://64.233.167.99 or any other will open the same website

6)This is because your ISP is probably blocking the alias not the address

7)Sometimes it may happen that the ip address is also blocked / blacklisted .

But IP address has multiple formats

1) Open a calculator (scientific mode) each numer seperated by a . (DOT) can be converted to any any other form eg. 

http://64.233.167.99

HEX ->http://0x40.0xE9.0xA7.0x63 or http://0x40E9A763 (not supported in some browsers)

OCT -> http://0100.0351.0247.0143

or any combination form http://64.0351.0xA7.99 is VALID

Decimal form is mostly not supported any more

For more info Refer http://en.wikipedia.org/wiki/IPv4

2) Tip Try flagfox an extension for firefox v useful

3)if your getting weird dns error or getting wrong ips from ping CHANGE YOUR DNS DONOT USE OPENDNS

4) There is one more trick which i am gonna let you figure out yourself