The Converter macro available at http://groups.yahoo.com/group/cat_conv/ (developed by Sergei Mouraview) and from this page too, automates the process of converting Excel glossaries into a Multiterm import file. It is fast and FREE.
You define columns exactly as you want records defined in your Multiterm database and the macro handles the rest.
Multiterm has the ability to handle duplicates on import.
How it works
Preparing the glossary in Excel
First column is English, second is Greek
Make sure there are no empty cells in your file
In the first cell of the first column you type Seg L=EN-US
In the first cell of the second column Seg L=EL
Close your glossary
Click on Twb.xls
Open your glossary
Select the two columns
Go to Excel -> Tools -> Export to TWB Memory
A text file is generated in the same folder. You import it to Trados.
Importing a glossary to MultiTerm 5
Use a similar procedure to create a MultiTerm 5 database with MultiTerm.xls
In first column you add English and the second one Greek.
Then go to Excel -> Tools -> Export to Multiterm