talk to Quazi or Davioware they are the brains behind that.
Yes, those are the famous Quazi Blobbers.
Basically this works with physics and some effects. So the liquid is actually formed from some orb sprites with physics behaviour attached. They have another orb sprite contained, without any behaviour. This would be the visual part of it, with some effects like colorise and tint plus slapped on the layer... if I remember correctly, but why am I even trying to explain it.
Take a look here: http://dl.dropbox.com/u/4322334/blober%20engine.cap
That's the original example file by QuaziGNRLnose.
There might be a faster way to do this soon. Since lucid is working on a liquid plugin. Looking forward to that!