Desktop Manager software is the program that gets installed on your PC
Handheld software is what gets installed on your BlackBerry(which gets installed on your PC first then installed to you device through Desktop Manager)
You want the newest version of both
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go here and put in your 10 digit phone number and get the newest of each, make sure the newest version of desktop manager is installed first then have it closed and install the latest device software.
then plug in, if you stil dont see your device, check connections at the top right. make sure its set to USB.
if still nothing, go to c:\program files\blackberry\appload and open loader.exe and try to update that way