Pattern Matching - Range of Letters

I'm sure that others have solved this but I can't find anything with my
(google and archive) searches. I need to retrieve data where the text
field is within a certain range e.g.
A-An
Am-Bc
Bc-Eg
....
Yi-Zz

Does anyone know of a good approach to achieve this? Should I be looking
into regular expressions, or maybe converting them to their ascii value
first?

Any comments are appreciated.

postgres 8.2.4, RHEL

Thanks
Ron St.Pierre