Um, no you don't. Nero's splitters and decoders are known to be buggy, slow, and have a stupidly high direct show priority.
Simply get Haali Media Splitter (
http://haali.cs.msu.ru/mkv/MatroskaSplitter.exe)... None of the bloatware of Nero, it's free, and it also splits Matroska (MKV) filetypes. As for the codec used, it's most likely an MPEG4 Part 2 (ASP) derived codec; DivX, XviD, etc, use this type, and you can easily (and quickly) decode these with FFDShow (
http://www.free-codecs.com/download_...p?d=1488&s=50).
Enjoy, people.