If the pop-ups came with the installation of LW then it's because the installer wasn't downloaded from the official site.
If the pop-ups came with the download of a file VIA LW, then it's because of what you dlded was infested with spyware/adware.
Try Spybot (it's a link. Click it)

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iMac G4 OSX 10.3.9
RAM 256MB
LW 4.10.5 Basic
ADSL anything from 3 to 8Mbps/around 1024kbps

"Raise your can of Beer on high
And seal your fate forever
Our best years have passed us by
The Golden Age Of Leather"
-Blue Öyster Cult-