I am using xypic with LyX 1.3.6-1 for Windows. Angus Leeming kindly showed me how to do this:
Place usepackage{xy} into the preamble and enter the xycode, e.g. \xymatrix{A \ar[r] B} into the lyx editor, then mark it and hit C-S-m. This works with most of what I need from xypic, but not with arrows that are bent upwards or downwards, e.g. when I replace \ar[r] with \ar@/^/[r] or \ar@/_/[r] or \ar@/^1pc/[r] Somehow, mathed does not interpret these key-sequence correctly. Any ideas, what to do ? H.Peter