The eb-1150 is only capable of displaying files in its native imp format. You can buy those from fictionwise (1/2 VGA Greyscale) or ebookwise.
You cannot use any other type of file at all. There are utilities for converting text, rtf and word documents to imp files. But you will not be able to display secured pdf, mobipocket or ereader files.
There are ways to break apart Microsoft Reader (lit) files and convert them for use on the eb-1150, but those tools will be illegal if you live in the United States as they are a violation of the DMCA.
Fictionwise:
www.fictionwise.com
Ebookwise:
www.ebookwise.com (all eb-1150 files and nothing else)
They also sell a librarian program (windows only) that does conversions of non-encrypted files.