errm... I think we're talking about a different kind of "splitter" here.
The latest freeware version of SolveigMM AVI Trimmer will handle MKVs - it's a rather basic program and a bit cackhanded to use, but it might do the job if your needs are modest.
SolveigMM AVI Trimmer worked great, cheers all.
This program seems to crash everytime now. Has anyone else got a solution to splitting a mkv file?
You could try MKV Merge