If you bought the Belkin F5U409, which is normally ridiculously overpriced anyway, and you have x64 windows 7 like any normal human being in 2011, you will run into this beautiful snippet when trying to download drivers:
Is the F5U409 USB PDA Adapter compatible with vista 64 bit?
No, this product is not compatible with vista 64 bit. It is compatible with Vista 32 bit computers. We do however have a similar adapter which is compatible with Vista 64 bit, you can use part F5U257 (USB-to-Serial Adapter).
They really have no shame.
As your gut tells you, this is not true - the device must work somehow. I found this fine post via Google, by a good sysadmin: