i *think* this is an indication that you aren't using Java version 1.5
 
open DOS or Terminal and type `java -version`
 
if you do have it, then something else is the matter. if so please post your operating system name and version, plus the version of java.

I'm having exactly the same problem on both my laptop and desktop.
Processing returns:
 
 java.lang.UnsupportedClassVersionError: org/rsg/carnivore/Log (Unsupported  major.minor version 49.0)
     at java.lang.ClassLoader.defineClass0(Native Method)
 
 Both are running WinXP and java 1.5...  
 
 C:\>java -version
 java version "1.5.0_08"
 Java(TM) 2 Runtime Environment, Standard Edition (build 1.5.0_08-b03)
 Java HotSpot(TM) Client VM (build 1.5.0_08-b03, mixed mode, sharing)
 
Thanks :)

ok i think i found it. you need to use the version of Processing called "Windows (Without Java)" on the Processing download page (http://processing.org/download). you should have a folder called something like "processing-0118-expert" -- it's better to be an expert i guess :)
 
the reason is if you use the other windows version of processing, it bundles a local version of java that's version 1.4. so even if you have java 1.5 on your PC, when you launch processing it's still running inside java 1.4.  
 
anyhoo... if you use the "Windows (Without Java)" version of Processing it should run inside whatever java you have installed (i.e. version 1.5) and the carnivore library should work fine.
 
can someone please post to confirm this works? the PC i have at home has a bum ethernet card, so i can't actually test this...

Thanks a bunch Alex, downloaded "Expert" version and it works well. It gives me this warning though, is it anything to worry about?
 
 
[org.rsg.carnivore.Core] Warning -- can't open device "\Device\NPF_GenericDialupAdapter" (CaptureDeviceOpenException)
 
Sorry to keep bothering you!

Ok, excellent. Thanks for the help. Maybe I'll have a client to post soon, no promises though.