is it possible for me to monitor and index a file situated in remote unix server in my windows7 5.x splunk instance.
If you can open a Windows file browser and use it to see the file, then yes, you can. That probably means that the file is on a shared directory.
If you can't, then you can install a Universal Forwarder on the unix server to collect the file and send it to your Splunk instance on Windows 7. Usually this is a better choice, anyway.