Have a look here, there are lots of tips for maximising your LW's performance
A few things to consider while configuring LW for optimal performance

What's your connection quality (poor, good, excellent etc)? Do you see the firewall icon (brick wall in front of the blue earth)? Download a file from here & see what speeds you get
http://www.magnetmix.com/video.shtml

I don't use iinet but there might be some people around who do. It sounds a bit like an ISP prob but AFAIK no Oz providers are shaping bandwidth yet