Did you try C:\Program Files\Microsoft Office\Templates\ without the 1033?

Recommended here:
http://office.microsoft.com/en-us/powerpoint/HA102140721033.aspx?pid=CH100668201033

I belive you know this stuff already, but I'm putting it here for others who
may be following along.

On Vista and PPT 2007, it's here:

C:\Users\echo\AppData\Roaming\Microsoft\Templates

(Of course, substitute your user name for "echo.")

On WinXP and PPT 2003, it's at C:\Documents and
Settings\UserName\Application Data\Microsoft\Templates , as explained at

http://www.soniacoleman.com/Tutorials/PowerPoint/powerpoint_2003__templates.htm

So it seems you're generally looking for folders Application Data (or
AppData) | Microsoft | Templates. If you use File | Save As and choose
Template from the "save as type" list, it should take you right to that
folder so you can know for sure.

This will make them show up in "My Templates" or "New From Existing" when
you choose File | New in PPT 2007. As for getting them into Installed
Templates, as you mentioned, those files are located at C:\Program
Files\Microsoft Office\Templates\1033. According to a Microsoft person
posting in
http://groups.google.com/group/microsoft.public.office.templates.misc/browse_thr
ead/thread/c165d25c986d291d/6dbd938164952f14?lnk=st&q=Johnbes+group%3Amicrosoft.
public.office.templates.misc&rnum=4#6dbd938164952f14 ,
" 'Installed Templates..'  shows all templates copied to your system during
Office 2007 setup." I also tried adding a template to that folder here, and
it doesn't add my template to the list that shows up on the "installed
templates" in File | New.

So I think we're limited to adding a folder structure to the "my templates"
area.