I don't know if it will run on windows, but there is a linux program called tellico that is a collection manager, ie a library. It is essentially a database for books. You will likely not want to run out and install linux just to use it, but I've got over 800 books cataloged and it works very well. see tellico.
Tellico is a Linux desktop application that does most of what you're asking for. It doesn't have a "hosted" component - it's not a web app or anything, it's just a standalone tool. The databases it created are simple files, though, and easy to copy around or host in a network share.
My wife and I have been using it for a while to manage our collections of books, comics, games, etc. While I don't think it has support for connecting to a barcode scanner, you can just punch in the ISBN by hand.
I think a wiki is your best options. You would have to be able to code to extra the data, store it in a db like mysql or sqlite, and then use a wiki frontend like foswiki or mediawiki. It would be important to note that you would have to create your schemas to that of the wiki you are going to use. Once you have successfully extracted your information into the appropriate schemas, you should be able to load the page using your wiki software like mediawiki. You would need to research the finer points, but this is probably less than a 20 hour project.
If that fails, maybe use something like Tellico? http://tellico-project.org/
On a Linux desktop, I like Tellico, which can manager collections in general (there is a built-in "book" category, but it may be necessary to create a custom "comic book" object; this isn't difficult at all, however).
For an Android phone, this app, which I haven't used, seems geared in that direction.
I use Tellico to manage my book collection. I enter in ISBNs, and then use the included Library of Congress tools to pull down title, author, LLC, etc. I don't have it in front of my right now, but I'm pretty sure there is a Worldcat API and it can pull in Dewey Decimal numbers. Occasionally, when it didn't work, I'd have to either pull up the record at a university library or make up the classification. The route for Dewey Decimal should be similar.
Apparently there is no plan to launch a version that is compatible with Windows. Source: http://tellico-project.org/does-tellico-run-windows
For years I ran dual operating systems on my personal laptop just so I could affordably catalogue my books and records.
I haven't been satisfied with anything so far. There are lots of websites that do it, but most of them are missing a huge chunk of games in the shared database.
I made a custom database in Tellico, but I never got around to filling it in. It's probably easier and faster to use an OpenOffice Calc spreadsheet.
See my post above about Tellico. It's powerful and free, but does require KDE. If he's not a Linux guy (yet), he can install KDE on windows, also free.
I'm not a used bookstore (yet) but have found Tellico (sorry, Linux+KDE only) to be amazing for keeping track of my tons of books. Just type in the ISBN and it takes care of the rest.
Very poorly indeed. I've been too lazy to catalogue my collection in any systematic way, but have done enough research to know that you can get software for collection management (Alexandria or Tellico; I'm a linux guy, btw) that allow for controlled lending. I think Tellico can even be configured to send reminder emails when books are overdue...
I recently organized my nonfiction collection. I used Tellico to first catalog my books. It let's you enter a list of ISBNs and it'll pull author, title, LOC call codes, etc. I then put everything in Library of Congress order. I did this because it generally breaks down by subject and author pretty well. Also, when I get books from my university library, they already have LOC call codes on their spine.