So now you got all the ones you had as a png in a seperate folder, right?
If so you can delete both mentioned folders (exit WLM first), the one for MSN 7.5 emotes and the one for WLM 8.1 (don't worry it will rebuild the folder) without loosing a single thing (will require adding the emotes that did work too). You can also delete all DT2 files that don't have a matching ID2 file if you prefer..but deleting the whole folder is easiest. Then add the emotes as you always do through WLM.
If not so follow these steps (or if above method confuses you):
1) Make a totally independant temporary folder (eg: C:\myemoticons)
2) Copy every .DAT, .DT2, and .PNG from the
"\Documents and Settings\<windows accountname>\Application Data\Microsoft\MSN Messenger\<ID number>\" and
"%userprofile%\Local Settings\Application Data\Microsoft\Messenger\<.NET passport>\ObjectStore\CustomEmoticons" directories to that temporary folder
3) Remove both messenger directories (as they are probably screwed up now anyways
)
4) Go to your temporary folder with all the copied files and rename every single file to .PNG if they aren't already named liked that
5) remove duplicates images if you have some (check with an image viewer)
6) start Windows Live Messenger and start adding the icons in the proper way by going to Tools > Emoticons > Create... > Find Image
7) remove your temporary folder
Edit: you're welcome
/ 
