sync data between MySQL and Postgresql

I think you should just configure Jasper to use mysql datasource.  That will be a way lot easier.  Go to section 4.1 of http://community.jaspersoft.com/documentation/jasperreports-server-administration-guide-v500

Ok. How can I get the sample data from postgresql to MySql

I don't believe you need to.  Jasper supports multiple data sources so you just add a mysql data source.  You will need to download the mysql jdbc driver from http://dev.mysql.com/downloads/connector/j/ and extract the jar file to the apache-tomcat/lib directory, restart tomcat (I just used the ctlscript.sh script to restart everything.)

In the data source definition you set Driver to com.mysql.jdbc.Driver and URL to something like jdbc:mysql://localhost:3306/test

That's as far as I've gone so far =)

Tx. Its the sample data that was an issue for us...

Again you can keep the postgresql data source with the sample data, then just add a mysql data source for your real data.  No need to transfer data from postgresql to mysql or vice-versa

I've also my own data that wish to transfer - how can I import data to Postgre?

Think you should file that as a separate question and provide details what exactly you want to do i.e. what is the format of the data, etc

Can one have links to 2x data sources in JasperReportsServer? Please elaborate
Again you can keep the postgresql data source with the sample data, then just add a mysql data source for your real data.  No need to transfer data from postgresql to mysql or vice-versa