Windows 7 (the RC build, 7100) no longer implements per-user key mappings: as Microsoft never documented it anyway, removing it is their perogative. This is unfortunate, as it's back to the days of Windows 2000 where key mappings apply to all users without possibility of exception and require administrative privileges to be created or removed. I can only speculate whether they were dropped because they were unsupported, or because they just wouldn't work with Fast User Switching, or accidentally, or they were in some way incompatible with the Windows 7 code.
It's a pain for me as KeyMapper expects Windows 7 to behave like Vista (*) and Windows Server 2008 and to implement scancode mappings in HKEY_CURRENT_USER\Keyboard Layout and so the program sets the mappings, we log off and on again, and Windows 7 then ignores the scancode mappings, and the key remapping fails and I get a very polite support email with 'broken' or 'doesn't work' in the subject line.
It's still possible to set mappings, though, in Key Mapper but you have to tell the program to 'show / boot mappings' from the Mappings menu and then authorise the Registry change and then reboot your computer.
So it looks like some new behaviour for KeyMapper under Windows 7 will be required. I might maybe just try and get a recent build of Windows 7 just to see if just maybe the RTM code will implement per-user key mappings before I even think about what to do (and how to deal with UAC).
(*) Because it's 'later' than Vista: Windows 7 was only a gleam when Key Mapper 1.0 was released.