I was looking to find the x64 equivalent of AlwaysMouseWheel
and just happen on X-Mouse Button Control
; it does what AlwaysMouseWheel
does and much more, has discrete x32 and x64 versions in the downloadable package, and seems to be portable upon extraction without any tricks; it is even able to make screenshots and save your desktop icon layout, something I find essential in Windows XP; I haven't tested it thoroughly but I'm pretty impressed with it.
Functions available to map to your mouse buttons includes options such as: send any keys using the simulated keystroke editor; launch any windows application; copy/cut/paste; media control (play/pause/stop/volume/mute, etc.); capture screen (or active window) image to clipboard; click-drag (sticky buttons/keys); Vista (and Windows 7) support with some Vista/7 only features such as 'Flip 3D'...
EDIT: I think the very professional looking User Guide
deserves to be mentioned, too. It's at http://mirror.highrez.co.uk/downloads/X-Mouse Button Control User Guide.pdf
Currently at v2.5 (changelog: http://www.highrez.co.uk/downloads/xmbc_changelog.htm