If interested in a lite client, try the http://go.icq.com
the reason it prolly doesnt let you install is because they might ahve changed some of their protocols from one realease to the next. or... try disconnecting from the network when installing the version you want to install - prolly wont work, but always worth a try.
and also, on this forum i have given details on how to stop the full version from displaying ads. If you want the full version of icq, you can run it without all the nasty ads. Just do a search on this forum for the posting about blocking ads, and there is a step-by-step how -to to remove the ads.
I found the thread here:
http://www.oldversion.com/talk/index.php?a...ct=ST&f=2&t=735