Hey,
With bits and pieces of old stuff lying around on your system it's possible there's a conflict - but these are usually very hard to identify. If you've uninstalled all the unneeded old ESRI SDK/programs then I suggest running some house keeping apps - such as Windows Disk Cleanup, Regclean and/or CCleaner - perhaps there are some old Registry entries which are preventing successful install of the data expansion pack. Essentially what it's doing is laying down a few extra DLLs which are required for enterprise Geodatabase access.
Regards
Mike