Since no one is answering your question, I'll throw out some non-scientific-wilda$$ guesses to start it off.
1/ perhaps you're asking that external to do too much?
2/ Linux, the Mac and the PC use different file systems.
3/ The PC may not be able to read the Mac partition without a third party utility.
4/ The PC may read from the Linux partition...maybe.
5/ Linux may not read from the Mac partition...unless thing have changed in newer distos. Linux can read HFS but not HFS+
6/ AFAIK, The Mac can not read, see or mount the Linux partition.
7/ Not sure about the overall state of FW support on PCs. Does the external also have USB2?
8/ I'm not sure, but can Linux be booted off of a FW external?
Someone will come along shortly to elaborate on my guesses...