Been running their Vista 2.3.6 driver dated 8/24/2009 for a couple of weeks on a Vista 64-bit system with no problems. Wireless router is a DIR-655. Works with Vista SP1 and SP2.
Ralink changed their webpage for drivers. It's now
here (or
Software -> Windows from their
homepage).
Since the DWA-140 uses Ralink's RT2870 chipset, you'll need the driver labeled "USB (RT2870 /RT2770 /RT307X /RT2070 /RT3572)" on Ralink's webpage.