Internet Explorer 7 is not supported on this operating system.

Download: http://download.oldapps.com/Internet_Explorer/IE7-WindowsXP-x86-enu.exe
(EDIT: Alternative DL link: https://web.archive.org/web/20190429231025/https://download.microsoft.com/download/d/1/3/d1346f12-f3a0-4ac6-8f5c-2bea2a184957/IE7-WindowsServer2003-x86-enu.exe )

In order to try to install Internet Explorer 7, the following steps were previously taken:

1) Set "Uniprocessor Free" in HKLM/Software/Microsoft/WindowsNT/CurrentVersion/CurrentType.

2) Edit: HKEY_LOCAL_MACHINE /SOFTWARE/ Microsoft/Internet Explorer and change "Version" to a number below 7 (ie 4.0.6001).

The first step is because it won't install in a checked environment, the second one is because otherwise it detects there is already a IE installed greater than 7.

Now proceed to install IE7, it will start unpacking and afterwards it will show a window saying "Internet Explorer 7 is not supported in this system".
The lines in the log shows:
fixme:(dll/win32/shell32/shlexec.cpp:1782) flags ignored: 0x00000004
err:(dll/win32/comctl32/commctrl.c:1936) GdiAlphaBlend failed: 0
fixme:(dll/win32/clusapi/clusapi.c:59) ((null),0006ED34) stub!
fixme:(dll/win32/advapi32/misc/efs.c:58) DecryptFileW(c:\b7d55ccb7a328223635f62bc5c7575b9) not implemented!
fixme:(dll/win32/wintrust/softpub.c:296) Cannot verify hash for pszObjId=(null)

Which seems as since DecryptFileW is not implemented it can't verify hash and fails. Or could it be a different reason?