You can block visual ads in Skype by blocking the IP addresses of the related ad servers.
I doubt this will block the crappy new audio ads, but I can't be sure until I run into them.
For US users, Skype currently pulls ads from these servers over port 80.
18.104.22.168/26, adlegend ad servers
22.214.171.124/24, msecn.net ad servers
126.96.36.199/24, dimestore ad servers
188.8.131.52/24, adlegend ad servers
184.108.40.206/24, adlegend ad servers
220.127.116.11/32 google ad server
18.104.22.168/32 google ad server
22.214.171.124/32 is the Skype Upgrade Server (block skype updates, not ads)The Microsoft Block (126.96.36.199/24) provides some legit services over https (port 443).
The ads are all over HTTP, so only block port 80.
I'll try to isolate MS's ad serving IPs in the near future and update the list.
One way to block by IP in windows, is to use IPSec.
It's tougher to learn than blocking by host file, but it can be more effective.
Here's a guide to IP Blocking, using IPSec in WinXP/2003. Vista/7 is similar.
Also: You can't block IPs using a hosts file, just domains.(subnet notes for newbie networkers:
188.8.131.52/24 = 184.108.40.206 - 220.127.116.11
18.104.22.168/26 = 22.214.171.124 - 126.96.36.199
188.8.131.52/32 = 184.108.40.206 - 220.127.116.11)--
The Dark Tower's Skynet evolves from 4chan.