I'm the original poster, and I appreciated the responses.

To respond to some of the posts:

I don't know how deep my sprinkler water lines are, and I can't speak
for my neighbor's lines, but I remember seeing my lines put in, and it's
at least over a foot deep.

Part of the problem, is that my neighbor has a 20' wide driveway, and
the cable guy said they need a certain machine so they can run the cable
UNDER the driveway. They really can't get it here any other way.
That also means that the cable won't be an inch or 2 under the ground,
at least not near the driveway.

If the cable company's box on the street was on my property, the cable
guy told me he could have just run a line himself instead of waiting for
the big boys with the big machinery.

I'm on a residential paved street, with a paved sidewalk, and some front
sprinkler heads are located next to the paving, which means that my
water lines run directly across the entire lawn. We don't know exactly
where any of the water lines are. Nobody does.

I know I'll have to ask the cable company about their liability, but it
just seems crappy to have to put a neighbor thru the hassle if there is
a problem ruining their sprinkler lines.