Well, there is another possible solution. You can reinstall Windows WITHOUT formatting the hard drive. If you simply installed Windows on top of itself (in other words, in the c:\windows folder like it probably is now), it will refresh your Windows files, and install DirectX or 6.1. Then you could go ahead and install DirectX 7.0a on top of that. Reinstalling Windows should take you about 45 mins or so.
Deleting DirectX 7 files is a tedious chore, and could result in blue screen errors. Actually, Microsoft says (of DirectX 6) the following:
--------------------------Microsoft Knowledge Base-------------------
SYMPTOMS
After you install the Microsoft DirectX 6.0 upgrade, you cannot remove DirectX 6.0 and revert to the earlier version of DirectX included with Windows.
CAUSE
The DirectX 6.0 upgrade for Windows is an update to the operating system itself; it is not an add-on component. The upgrade cannot be removed.
RESOLUTION
To revert to the earlier version of DirectX included with Windows, you must reinstall Windows from MS-DOS.
-----------------------Microsoft Knowledge Base----------------------
In other words, they're clearly saying that DirectX is no longer just an add-on, but actually part of Windows and can't be deleted as such.
So, I'd opt for reinstalling Windows (don't format or erase your hard drive, just reinstall Windows on top of itself) and then upgrading DirectX 6.1 to DirectX 7.0a.