Is it possible to plot multiple curves which have different x-values ?
Yes, definitely. This question comes up fairly frequently, and always puzzles me since the default for almost all input methods is unique X values. How are you creating your plot?
Or, is there a skip capability for each curve for certain values of x ?
When you open the file check the "Pick columns to plot" box on the Open dialog. On the next screen check the "Alternating X,Y columns" box. If that box is greyed it's because there are an odd number of columns (or, more specifically, an odd number of columns that can be translated to numbers).