Did you know WinXP has built-in support for Vietnamese keyboard input.

Back on the old days before Unicode came out, there are some pseudo standards for Vietnamese fonts and input interface. The problem is they don't work in all applications and you need to download proprietary application to be able to type in Vietnamese. Not anymore with WinXP. WinXp has support for all kind of languages included Vietnamese. You just need to turn it on. Go to Control Panel/Regional and Language Options/Click on Languages tab, check both of boxes under Supplemental language support. WinXp then asks you for the CD to install some files. If these boxes already checked you may skip this step. Under Languages tab, click on Details and choose Add. Under Add Input Language dialog box, choose Vietnamese and hit OK. WinXp will add a switch box either in your task bar or Desktop for you to switch between English and Vietnamese. I would also set up the Preference's Key Settings to switch between English and Vietnamese.
OK and now how to type in Vietnamese? You need to see the keyboard layout. You can see the layout with WinXp's On-screen keyboard. Click on Start/All Programs/Accessories/Accessibility/On-screen Keyboard. Don't forget to switch to Vietnamese input first.
Here the screenshot of the WinXp's On-Screen keyboard in Vietnamese typing mode