Hi Arch,
Your question is not terribly clear to me -- but I'll try to answer it, anyway (if you don't mind :-)
I believe you are using OC4J (I assume stand-alone version -- and not the one embedded in "JDeveloper" -- but I don't know what version number) running on a Windows machine (but again, I don't know which version of Windows) and that you want some component in your application (that you have deployed to OC4J) to write log messages to some file that is supposed to reside on another, UNIX machine (yet again, I don't know what UNIX version nor what type of machine) which is situated on the same local directory (i.e. LAN) as the Windows machine (that is running OC4J).
Assuming the above is correct, then you have two possibilities (in my opinion):
use a file URL which has the format: file://host
ort/path/to/filecreate (and use) a network mapping for the UNIX machine from the Windows machine. At my place of work we use "samba" software to do this. Unfortunately, I don't know much about it (I just use it). However, your problem may also have to do with permissions. The Windows user (that "owns" the OC4J instance that is running) may not have permission to create files on the UNIX machine. But yet again, I can't help you with a more detailed answer since I didn't find enough information in your question to allow me to.
And if the above is totally useless to you, then please excuse me.
Hope it helps (anyway).
Good Luck,
Avi.