Jacky Mok just posted a link to the system requirements for the soon to be released Windows Live Suite apps, and they include 64bit support, but only if you're running Vista. from Jacky's blog post:
Windows Live, Live Suite, Installer, Windows Vista
Platform 32 bits 64 bits XP SP2 Yes No Vista Yes Yes Vista SP1 Yes Yes 2003 Server No No
32 Bit Includes: Mail, Messenger, Photo Gallery, Sign-in Assistant, Toolbar, Writer, Family Safety,
64 Bit Includes: Mail, Messenger, Photo Gallery, Sign-in Assistant, Toolbar, Writer
The installer should auto detect the architecture and omit Family Safety if you are on 64 bits.