That really sucks, but are you really sure it´s ICQ causing this?
I ask, because i know for a fact that MSN Messenger open up doors for all sorts of garbage, including a few nasties that will use your machine for sending out spam.
I´ve lost count on how much crap i´ve had to remove from my wifes machine, and all of it came through messenger. I personally don´t use it, so i don´t have that problem. :)
With ICQ on the other hand, i´ve never had any problems, and i´ve used it since 1997
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Windows safety has never worked as intended and unfortunatly Vista is no exception, so it´s more or less pointless having it running other than for using resources. 
As for AVG, it´s free, but sadly you also get exactly what you pay for. A guy at work has a bad habit of installing that program(despite my warnings), and apart from never ending error messages,(boot errors, missing dll-files etc),  it slows down the machines.
If you have the chance, you should really try out Nod32 instead. You wont even notice when it´s working, and it blocks any file that has the characteristics of a virus.

Rudolf Herczog
Digital Artist
www.rochr.com