WIFI problems after 10.5.2 Software Update

This issue has been affecting a lot of people with various different routers. I sorted my issues out thanks to this page:

http://discussions.apple.com/thread.jspa?threadID=1389855&tstart=0

So I post it here in the hope that some of you can find it useful.

A solution is to:

Log into the wireless router and drop the fragmentation threshold and the frame threshold to 2306.

Can't find the settings in my router - 3com model. Funny, cos the problem only happens on my iMac, not my macbook even though they're both using the same wireless network.

you'll need to connect your router by ethernet cable to access the settings. And you'll need it's IP address - usually this is 192.168.0.1 or something similar. Type that into your internet browser where you would normally type in www.anything.com then that should bring you to your routers home page where you can then look for your settings.