after getting new 17" tires i had the same
steering wheel vibration at highway speeds
that alot of others have experienced.

but after experimenting to isolate the problem
(ie. putting on my old stock rims/tires and
noticing how smooth the ride was to confirm that
it wasn't a mechanical problem),
it was as simple as getting a "dynamic" balance
versus the "static" balance that was done.

the dynamic balance put both clip-on weights
onto the inner rim of the wheel "plus" tape weights
just inside the spokes near the centerline of the rim.
i guess this distributes the weights better, though
it takes the technician a lot more time.
it made a world of difference.
in addition, i got hubcentric rings specific to the
wheel and car and that took care of the last little
bit of vibration.

hope this helps.