Both will be very problematic as they use port 80 and unpriv ports for authentication/communication. But it's NOT impossible...just takes work.

Believe you me, I went through all of this a year ago at home with my teenage daughters. I finally was able to block AOL, Yahoo, and MSN, but with a mixture of several things. I just don't think a Netgear will do it for you, but someone may prove me wrong...

For AOL, using IPTables I blocked port 5190 in and out, and anything going to login.oscar.aol.com, and then I also added any website aol had where you could download AIM into squidGuard (works with squid proxy server, all of this runs on Linux) so that I could block any attempt to download the client. All the kids would get was a nice little page that said...go away....

For Yahoo I blocked every IP address Yahoo was known to use for messenger services using IPTABLES. I also blocked port 5050 in and out. I don't have the list of ip's handy, but I could post later on if you want. I also add all associated web sites for yahoo messenger to squidGuard for the same reasons as AIM above....

Now....MSN was the tough part. No matter what I tried, I had the hardest time blocking it. The thing that did the trick for me was a squid.conf entry that goes like this:

acl kids src 192.168.0.10/255.255.255.255
acl msnmessenger req_mime_type ^application/x-msn-messenger$
http_access deny kids msnmessenger

Then, on your network, you have to force your user browsers through your proxy cache, either by browser config, or by transparent proxy (I chose the latter using IPTABLES).

Worked like a charm.