As per my knowledge the sequence is not at all important. The significance of rigid modes is that you can see any unknown constraints etc. If there no constraints model is complete free, then your rigid modes zero or nearly zero value. This rigid body mode frequencis gives you a idea about the...
Maybe you try the import wizzard.
From file menu choose "import data..." and
then select the file and column separator (in your case space) and follow the further steps.
Cheers
