Typing Windows XP
Click Start, click Control Panel;
Note: In category view select Date, Time, Language, and Regional Options and click Add Other Languages.
Click Language and Regional Options;
Click Regional and other Language Options;
Click the Languages tab;
Under Supplemental Language Support, check the box next to "Install files for complex scripts and right-to-left languages"
and then click Details.
To add Greek:
Under input language select Greek, under Keyboard select Polytonic Greek. Click OK, click Apply, and then click OK.
To add Hebrew:
Download the SBL Biblical Hebrew (SIL) Layout (here). Open the .exe file BHebSIL (this will install the necessary files for the keyboard). Click the file entitled Setup. After a few moments a box will appear confirming the installation. Click Close.
On the taskbar a small box with the letters EN should now be visible. This shows the current input language (i.e. input method). EN represents English, EL represents Greek, and HE represents Hebrew. To toggle between keyboards simply push shift and alt at the same time.
See Add an Input Language on the Microsoft webpage for more information.