I had an earlier BB (7100) but have just got an 8300 but the version of Desktop Manager I had installed won't recognize the new device. I tried installing the software from the CD with the 8300 but the start.exe falls over. I went the the download ares to get the app direct from RIM but the SP2 version of 4.2 is >200Mb and the standard 4.2 version only installed the device manager and not the desktop manager (but un-installed the earlier version).
Hope someone has some ideas as to how I can get the 8300 working with my laptop.
Managed to get SP1 version of 4.2 downloaded and installed and it picked up the BB straightaway. So, looks like I needed some additional drivers. Manged to restore a backup onto it, so everything looks OK at the moment.