Try this Software Keyman 6.4 (Fully Registered)
http://www.4shared.com/file/123008023/ded8b264/Keyman_64.html
Installation & How to Use Tutorial (Sinhala Version)
http://www.4shared.com/file/123006531/cfd957d1/Keyman.html
It's very Easy to Use & Very Helpful. Try This. It's Work with XP & any Microsoft Office Package. It's Support with any Wijesekara layout Sinhala Font. I hope You Like it.