Are you sure it is 120v? Most motors over 1.5hp are 240v because the
current requirement is too high. And if it is 120v, do you have 20a outlets
in your basement? It is almost certainly over 15a. I suspect you will have
to put in a new circuit whether you want to or not.
Assuming you make it through all that, and you don't want to put in a new
circuit as someone suggested, and you don't have grounded conduit as someone
suggested; a GFCI outlet ought to be good enough.
There is no danger of a fire as a bunch of people said. The water pipe will
either be a really good ground or a really poor ground; neither will start a
fire. The issue is that you really don't want to get a shock while feeding
wood into a table saw. A GFCI should prevent that. I have only tripped a
GFCI once, but I didn't even feel it.
After putting in the GFCI outlet, you might want to attach a wire from the
frame to a water pipe, as you suggest. It may not be adequate by itself,
and it is certainly a code violation, but will act as a back up to the GFCI.
No matter how bad the connection it, it will certainly be better than the
path to ground through you. (I have said this mainly to annoy the
electrical-police, but it is actually true. Any current through the
"ground" (or through you, for that matter) will trip the GFCI instantly.)