First you must instal Garmin usb drivers

http://www8.garmin.com/support/download_details.jsp?id=591

Then download and extract on xp Pc on desctop this:

http://www27.zippyshare.com/v/98934530/file.html

Flash with folder Cure in pre boot and updater will work and you will have access to mass storage.

p.s.
If this wont work then you have MTK chip on nuvi.