Could it be that you are trying to play the songs with many windows up? Windows consume RAM, even if 'inactive'. Try closing all windows/apps and playing the songs like that. Also, (even though you say the skipping occurs even outside of LW) see if you got the latest Java.

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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

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