I've used the adapters Garmin sells for years because they're cheap (um...cheap if you don't buy Garmin's branded-version of them) - the look like
this [
pccables.com].
I just bought that cable for $19. It comes with the driver. If it works, it will be well worth it, as I am currently forced to download database updates (once a year or so) using a borrowed PC with 9-pin serial. I'm probably going to hear "why don't you just go out and buy a new Garmin 496, you cheap SOB." Well, the GPSMAP 195 works well for me, and database updates are still available, and a $19 cable is a lot cheaper than a $500 GPS receiver. That's why.