I use a desktop PC with windows 7

My keyboard and mouse is wireless Logitech and works fine..

I have a second keyboard for my thai wife to use with Thai letters, so i have pluged it into the usb port in the front of the PC and it did the download thing itself , all is good ...BUT it is still in english letters, I wish it to type Thai for my wife to e-mail her family and friends ..

Please any help in changing it over , I had a good go ,but my knowledge is limited in this stuff.
Regards and thanks for you help

BB