Is there any way through which I can exchange data between two organization. I want to do my coding in Plugin only. Can we write a code in plugin by which it accesses/manipulates the data of a different org through web services only and not directly hitting its database. In know the orgs are different worker groups. Just wanted to know if its possible or if there is any other technique. Thanks in advance.
The data for each CRM organisation is exposed via web services which differ slightly for CRM 2011 and CRM 4. The best thing to do is download the latest version of the SDK for the target platform as there are several examples in there for plugins and service based operations.
From your plugin you will be able to access the other organisation via this service and a connection to the service for the "local organisation in which the plugin is running will be available from the IExecutionContext parameter passed to your plugin. Any operations you carry out across both orgs will not be transactional though.
Also be sure to take a look at the sync and async options available for the plugins. If their use is appropriate for your scenario consider using an async plugin for the updates to the target org to minimise their effect on the source org.