There is a growing popularity of 64-bit window systems versus the standard 32-bit. The difference has to do with the architecture of the computer and the size of the registers stored in the CPU. 64-bit systems are supposed to be more powerful, but most software has been built for 32-bit systems. Unless they are adapted to 64-bit systems, they often do not work. This is the case with much Unicode Tibetan Input software. TISE does not work for 64-bit systems, nor does Wylie Word.
Solutions to the issue of inputting Unicode Tibetan on 64-bit systems has not been extensively researched. There is, however, a free solution: Denjong TibType. This input systems works in Windows 7 64-bit as well as 32-bit. It works much the same way Tise does. Documentation and download from Denjong TibType. A for-pay solution is that of Tavultesoft Keyman and the keyboard provided by THL on the Keyman Keyboards page.
Another possible solution may be if it is possible to run a 32-bit virtual machine on a 64-bit host system. VMware has developed virtualization software for 64-bit machine, according to their announcement. However, this is not free solution, and probably means buying a second whole system, which is unpractical.