Installing Profiles
To use ICC profiles, first copy them into these two locations for Windows (2000 or XP):

C:/Program Files/Common Files/Adobe/Color/Profiles/Recommended

or these two locations for Mac OS X:

Library/Application Support/Adobe/Color/Profiles/Recommended

and these two locations for Mac OS 9 and Classic:

System Folder/ColorSync Profiles
System Folder/Application Support/Adobe/Color/Profiles/Recommended

The first location is mandatory for each OS and the second location is useful if you'd like these (or any other) profiles to show up at the top of lists in Photoshop. Putting a profile in both locations will not cause the profile to be shown twice in Adobe's lists because they check for duplicates while making their lists. So you might want to only keep those variants which you are apt to use often in the second location.

Windows users must quit and re-launch Photoshop to get the profiles to show up. Should you need to replace a profile with an updated version of it which goes by the exact same internal name, then you will need to quit and re-launch Photoshop, even on a Mac.

If you still use any Classic apps on a Macintosh, be sure to also add the profiles to the old System Folder's ColorSync Profiles folder at least, or put an alias of that folder into your OS X main profiles folder.

When profiles are listed in Photoshop and in most, but not all imaging applications which are ICC-aware, the name of the profile shown in the list is an internal name, not the actual file name of the profile. Usually both names are the same, but when they aren't it can be quite confusing! In OS X, if you double-click a profile, that will launch ColorSync Utility and you will be able to click on the desc tag in the profile and see its internal names (up to three different ones are possible!).