Excellent work of packaging the Urdu word lists from different sources. Not only that, Kashif has for the first time started work on the language grammar rules ("aff" file used by spell checkers like "Hunspell"). Help from Urdu language and grammar experts is needed to further this work. The installer is flawless.
To answer a later question about "how to use it?": Despite its name, it is a spell-checker not a dictionary. While writing on a website (in a text box) like email etc, right click and select "Urdu" in "languages." Now when writing in Urdu, misspells will be underlined by a red curly line. Right clicking on the word may suggest a correction. Remember any word not in the dictionary will be flagged (this may not be a mistake, just that the word is not in the dictionary. If you are sure about the word spellings, right-click option will allow the word to be added to your local list).
Also if you are going to write Urdu, make sure that you have BIDI enabled in Firefox. Help on this is available on Urdu wikiepedia: