>>There are several ways to do this...
>>http://fileforum.betanews.com/detail/Clean_Messenger/1142298266/1
>>
>>...one of the more popular ones is this one:
>>http://www.msgpluslive.net/download/
>>
>>If you use the 2nd one there is an option upon install to NOT install the sponser app (don't install it).
>>
>>Personally, I use Trillian Pro so that I can have MSN, Yahoo, ICQ, Yahoo, AIM, Jabber and GoogleTalk all in one client.
>>http://www.trillian.cc/
>>
>>..and there are other clients like that which are 100% freeware, such as Miranda:
>>http://www.miranda-im.org/
>
>So, basically, all those are software that need to be installed which are compliant to Windows Live Messenger providing a similar interface. Some of them requires to have Windows Live Messenger installed. But, I was looking for a way to use the existing software without seeing the advertisements such as subscribing to Microsoft on a specific service.

The Trillian and Miranda ones are messenger clients that do not require having any version of messenger installed.
The other ones are basicly hacks for the messenger that get rid of all the ads. If you want to use the standard MS client then you'll have to apply one of the hacks.