I own a Targus PA088U Serial to USB adapter, which I use to connect to devices such as switches and routers. I've had it for a couple of years now, but it is still a current product.
Having recently moved to 64-bit Windows 7, I've discovered that the drivers for it don't work on 64-bit Windows, and when I rang Targus they couldn't give me an ETA or even confirm that they are working on 64-bit drivers.
Come on, Targus, that's pretty poor. 64-bit versions of Windows have been around for about five years now! Rant, rant, rant ...
I've ordered a Tripp Lite U209-000-R which claims to support 64-bit Windows 7, as a replacement. I'll let you know how it goes.