I tried to sync several playlists from PC to BB via mediasync - more convenient (less crashes) - but MUCH slower IMO then a direct card insert into the PC.
FYI - I discovered with >4GB SDHC cards you need to download/install an windows XP patch (if that's what you're running - this is the problem) to allow it to be recognized by XP.
Here's the link:
Some Secure Digital (SD) cards do not work correctly on Windows XP-based computers
Sorry above is the KB description.. this is the download site for those that just want to get the patch (FYI - you'll need to go through the dreaded windows validation..)
Download details: Update for Windows XP (KB934428)
Hope that helps.