I recently downloaded DNG profiles from Adobe and also their profile editor. No trouble installing and using the profiles in Lightroom. However, when using the editor and then naming and saving the receipt I can't get the new profile to showup in Lightroom. I suppose I'm not saving to the correct folder.
From the DNG profile editor on labs.adobe.com: http://labs.adobe.com/wiki/index.php/DNG_Profiles:FAQ#WhereInstall they are in:
"On Windows 2000 / XP: C:\Documents and Settings\All Users\Application Data\Adobe\CameraRaw\CameraProfiles"
translated in Vista/7, it should be in: C:\ProgramData\Adobe\CameraRaw\CameraProfiles -and it might be a hidden folder- (according to a google search )
Hope this helps!