Bicycle Tutor

Hi,
I'm trying to remove a raiser from an old mountain bike with a threaded headset(I'm guessing it's about 15 years old) It looks like it might be this one on sheldon brown, but I can't be sure it's the same thing:

I've tried removing it by unscrewing the bolt and hitting with a hammer, as I thought it could be fixed in with a wedge. It seems to be stuck though. I wanted to check if there's any other way it might be fixed in before I try hitting it harder, in case I break something - any suggestions?
There's a strong possibility it could just be rusted together, so I was also wondering if there are any tips for freeing up parts which are rusted in. I've oiled it but was wondering if there's anything else I could do?
Thanks for your help!

Try spraying some WD-40 or liquid wrench down there and let it soak for a while. Then tap it lightly with a hammer to loosen it up. As a last resort you could pinch it firmly in a vise clamp and rotate the other end of the fork. If none of those work and it is rusted tight, you'll have to get it cut/drilled out.

Thanks for your swift reply Alex - I'll get the WD-40 on it!
Thanks for making such a great site too, your videos are really clear and helpful.
E