Apparently Microsoft Reader is being discontinued: Here are the details from PCMag.com:

The free, but extremely outdated, Microsoft Reader software will be discontinued on August 30, 2012.
Microsoft, however, will shut down its eBookstore on November 8, 2011, so stock up now on those .lit files.
Microsoft Reader launched in 2000, long before dedicated e-reader devices came into existence, and was one of the first applications that allowed customers to quickly download e-books for viewing on LCD screens.
“Microsoft Reader 2.0 lets you curl up with your PDA and read the same titles as on your Windows PC,” gushed PC Mag writer Konstantinos Karagiannis in his review, circa 2001.
Microsoft Reader supported .lit filetypes and was also the debut for Microsoft’s ClearType font, the closest semblance to digital paper at the time. When it launched, its only formidable rival was Adobe Acrobat eBook Reader, but over the years, it faced competition from more advanced e-book formats like eReader, Mobipocket Reader, EPUB, Kindle, and the iPad.

I heard about this yesterday, so with the help of Jane from Dear Author, I managed to strip the DRM from my Lit books that needed it, and converted them using Calibre. They are all now downloaded onto my Kindle.