Create a second date column in the worksheet, with the same date and
the format YY, and use both columns to make the date axis. This will
display correctly.
Correction: will display correctly in 97. Having just looked at it in
2000, I see that the "improvement" that forces double-columned category
ranges to look like those ugly Pivot Charts, with the combs cluttering
up the space.
So, plan B: go back to one column, format just the months you want with
"mmmmm yy" (space, not hyphen)
leaving the rest at "mmmmm".
Then set Chart Options.. Axes to "Category", and set Format Axis to
"Linked to source", then ensure that the months are packed too tightly
to allow the year to appear in the same line. It will wrap down to the
second line and appear as
J
08
which is how you want it.