Set default file association for all users

Hi I would like tiff files to be opened by internet explorer for all users. I am a little puzzled how to set that in the registry. I want to apply this to over 20 computers so that no matter who logs on, the tiff files will open with IE. We are using an application called Alternatiff that is tied to IE that handles tiff attachments in our applications. The application (Alternatiff) uses IE to open the tiff files hence my wanting to hard code that into the registry for all users. Thanks in advance. GPO is not an option at this point.

Set it up on one machine then search the registry for Alternatiff. Export the ones that have to do with file association. Import into the other computers.

Control Panel, Default Programs, Associate a filetype or protocol with a program.

Scroll down to .tiff and set it to open with Alternatiff.

Thanks Ztruker, the issue with your suggestion is that it applies to per user (HKCU). I did however try your suggestion prior to my initial post. I need to figure how to edit HKLM so that it will set for the machine. I already deleted all the profiles using delprof2, so any "open with" (hkcu) file association options have set by other users are gone. Once I figure how to set it in the reg under hklm, any subsequent logs will not have to set the open with options.

I really to take a class on registry scripting. Thanks Alejandro, but if I am correct in my interpretation/assumption, but doesn't HKCU apply to that specific user's key. That being said, how can I apply that to the other users' keys, especially since there are no profiles (I deleted them so that HKLM can take initial precedence)? So, (excuse my laziness), to assign .tiff to IE, would it look something like this (and work globally for all users)?
Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINE\SOFTWARE\Classes\.tif]
@="\"C:\\Program Files (x86)\\Internet Explorer\\iexplore.exe\" %1"
"PerceivedType"="image"
"Content Type"="image/tiff"

[HKEY_LOCAL_MACHINE\SOFTWARE\Classes\.tif\OpenWithList]

[HKEY_LOCAL_MACHINE\SOFTWARE\Classes\.tif\OpenWithList\ehshell.exe]

[HKEY_LOCAL_MACHINE\SOFTWARE\Classes\.tif\OpenWithProgids]
"TIFImage.Document"=""

Lol, so can I distribute the above reg export (as is) out to other computers, and it become the system wide setting for tiff files to open with IE? Or do I need to edit it (and how please)?

Awesome I will give it a try and report back.....thanks for everything.

Well, I tried that reg key and it did not work. So, I am going to try the instructions on this site, but still a bit unsure....but gonna monkey with it anyway.
File Association Example (Windows)