Heres a great little tool from ‘Cloud Jedi’ Joey Chan, which converts a 15 Character Salesforce ID, to a 18 Character Salesforce ID  https://cloudjedi-developer-edition.ap1.force.com/SalesforceIdConverter

For further information on ‘why the heck would I want to do that’, see this updated post

http://www.philwaltonconsultancy.co.uk/salesforce-tip-of-the-week-25th-jan2013/