MSN Messenger disconects all the time...

I searched for any kind of solution before posting...

The thing is:
I share my internet conection with my brother's computer, via local network. Usually, when my computer is on, my brother's session on MSN Messenger closes, and he starts ranting about it. It also happens with me, the diconection, when my brother navigates through the web (he opens as much IE windows as he can). MSN Messenger session starts and stops on regular basis, until we are both tired and mad.

I didn't have this problem a month ago, is basically recent. I'm with Windows XP and my brother has Windows 98, both with ZoneAlarm. Any clues?