Hi,
I have read your requirements and have some comments/questions below
1. Do you need the ability to do the word jumber solver as well?
2. In order to save the popularity of words, best methods is to save them in a database to increase the speed of programs. (If you save the words list in a text file, any change need to rewrite the text file which is around 2.5~3 MB). If you don't want to use a database, I suggest we use a text file which is a Frequency Word Lists, and do not change it; thats mean you cannot add, remove word and cannot change the popularity.
3. If you want to do it with database, I suggest we use Microsoft Access, and using VB.NET / C# to connect to it through OleDB.
Regards,