@Pal - You will need to use the setTemplateId to link the email message to the mail template and use the the SingleMailMessage class object to setup the mail. MassEmail message does not support use of templates. Please be aware of governor limits though. I think you will be limited to 100 emails in a single sendEmail call and 10 sendEmail calls in a single transaction.
Hi Pal,
The following thread talks about how to send email using batch apex, go through when you get a chance:
http://boards.developerforce.com/t5/Apex-Code-Development/send-a-mass-email-using-batch-apex/td-p/407637
Link for reference:
http://www.salesforce.com/us/developer/docs/apexcode/Content/apex_classes_email_outbound_single.htm
You can get your requirement here
http://www.salesforce.com/us/developer/docs/apexcode/Content/apex_batch_interface.htm
If this post is helpful please throw Kudos.If this post solves your problem kindly mark it as solution.
Thanks