Urgent headset help needed

Hi all,
Today I went to replace the headset on my giant, all was going well until I tried to free the lower bearing, the bearing has rusted and welded itself in, the lower part of the sealed bearing has split off along with the ball bearings leaving the top part stuck in place. I tried to hit it out with a punch from the top opening of the frame but it is flush with the inside of the frame so you cannot get any purchase, I also tried drilling it but the drill bit didn't even make a scratch. I was going to try heating it with a blow torch but didn't want to risk damaging the frame.
Has anyone else had this problem or got any ideas what I can try next?
Any help appreciated. Thanks. Gaz

im not an expert i could be totally wrong but i would wd40 it, and if that doesnt work then put the headtube end in a bucket of ice it should make the metal contract freeing the headset.

Thanks for the ice tip. I tried using a release spray but to no avail. Looks like I'm gonna be making a lot of ice cubes!

I had the same problem once - ended up being sorted with a dremel tool ever so gently different places cutting slices in the bearingcoverthing until it structurally weakened - beware of not cutting in to the headtube.

Thanks for the tips, I've got a dremmel somewhere so I'll have to try that, but as for the ice method, do you think plumbers pipe freezing spray would do the same trick?

Hi all,
Thanks to your advice all is now sorted! I managed to remove it using a combination of all the tips, it went something like this. Whilst I was waiting for the ice cubes to freeze (badmanlongtime) I soaked the headset in release spray, after snapping the tips off 3 screwdrivers I decided to get the dremel out (thuekr), after cutting about 1/4 inch worth of little slots I managed to break them off and with it structurally weakened it finally came free :-)
So, thanks to your help all is good! Oh, and if your thinking he didn't use badmanlongtimes ice cubes.... They're now in the G&T I'm supping whilst writing this.
Once again. Cheers!