adding tags

[NeoToxic]

how do i create a new tag to appear like were add image and hyperlink ect is? its for a hide hack so i would like it so when they click the image for the custom tag it opens a box Enter Url Here they click ok and it automatically posts it on the forum like below

Download:
[hide]http://www.urltheyentered.com[/hide]

Also the hide tag work work if anything like text ect is add after [/hide] is there a way so if they do add something after it and try post a message pops up saying eg. dont add anything after the [/hide]

Thanks for the help in advanced.