During the testing of the native Windows Mobile version of the current Opera Mini 5 beta (see THIS for more info), I've routinely tested it on my old, WM2003-only iPAQ 2210 Pocket PC.
Of course, the CAB installer didn't work as it's compressed; nevertheless, after manual decompression, the app itself did. That is, it's fully compliant with both WM2003 and WM2003SE, which is great news for all users stuck with those old operating systems and not having received any WM2003(SE)-compliant browser for ages. (AFAIK, it was Opera Mobile 8.65, almost three years ago, that still supported the OS – nothing after that, except for, of course, the PIE plug-ins.)
Therefore, I quickly remade the CAB file so that it also runs under WM2003(SE). It's HERE for download. (UnZIP it before installing!)
Here's a quick tutorial for anyone wanting to do the same:
1, in order to decompress the original CAB file (along with its INF file), download MSCEInf from, for example, HERE
2, in order to recompress the new and, now, WM2003-compliant CAB file, download CabWiz. It's part of Visual Studio and can also be found bundled with many CAB creator tools; for example, QuickCab 2.0 available HERE. Download the latter; you'll only need to keep the two cabwiz.* files (cabwiz.exe and cabwiz.ddf).
Incidentally, should you just quickly want to deploy some files in some predefined places (the app doesn't support relocation) and/or make some changes to the Registry, feel free to play with QuickCab itself. For our needs, it's not adequate as it doesn't support relocation, while Cabwiz does. Therefore, we only need to download it in order to extract the CabWiz files from it.
3, decompress MSCEInf anywhere on your PC; run it. Drag-and-drop the original, WM5-only CAB file in it.
4, click the „Extract CAB Files with original names in a folder” icon (the 7th on the toolbar from the left). Unpack the files to a previously empty directory anywhere. It'll, in addition to the files, create an INF file, containing the names of the files to pack, the shortcuts to create, the strings needed for installing the app in any other place than the built-in RAM and so on.
5, copy the two cabwiz.* files in the same directory where the just-generated INF file resides and enter „cabwiz name-of-exported-inf-file”. The CAB file will be created. As the cabwiz.ddf file defines cabwiz's output as uncompressed (see the Compress=OFF flag in it), the file will already be compliant with pre-WM5 operating systems.
Note that you'll need the excellent and free CabInstl app to install the app on any other location than the built-in RAM.
Also note that I've also tested Opera Mobile 10. Neither beta 1 nor the final version are compatible with WM2003(SE).