<<< Are there any suitable routers out there? >>>
I cannot think of a reason why *ANY* router shouldn't work with XP or Vista 64-bit. A router isn't installed in a computer, either as hardware or as software, it is a stand-alone network device to which computers (Windows, Linux, Mac) running TCP/IP protocol connect. The operating system is immaterial.
Now, USB ADSL Modems are an altogether different "can of worms". Also, what you will need are (64-bit) drivers for your PC's Wireless Network Adapter.