Antenna Questions

[jsbihn]

Hey all,
I have an '03 with the antennas on the roof, and I am looking to do a couple of things.
One I would like to change out the stock antenna for something different. I heard there is nothing out there that will fit it.... is that true? If not, how do I put another antenna on. I am looking to put possible a longer antenna or maybe even the long flexible tye to try and get better reception.... or if not just be able to put another shorty on there without having to spending the 50-60 bucks for one from the stealership.

The other thing I would like to do is remove the Onstar antenna. I am removing my Onstar and since I am.... welll i dont need the antenna there any more.
Is there a plate or a cap or something that came from the factor to cover this once removed?

Thanks all