Microsoft originally released Tweak UI as a value add tool with Windows 98. Since then, its popularity has grown and its usage expanded, and with it, its power as well.
Today, Tweak UI is the best tweaking tool out there for the important changes, and Microsoft has refused to provide official support for it. While that is not an issue, and there are hundreds of support websites on the web, the fact that Microsoft has not yet released a version compatible with the ever-growing true 64-bit PCs is.
Starting with the AMD series and the upcoming Intel series, x64 brings new power, and requires updated programs. So, if you are looking for Tweak UI for AMD 64-Bit processors or Windows 64-Bit Edition, download it here!
The optimizations currently hold only for AMD and Intel EM64T's. What this translates to is no Itanium support. Microsoft has realeased its own version for Itanium, which you can download at their Powertoy website. Please note, this will not run on Windows x86: you will encounter a series of errors, and it just wont work. Supports Windows XP and 2k3 only.