Dexter:
You said: "I run a comic fan site"
And then you said "I need a multiuser application for the web that people can log in ... "
Does this mean that you already have a Web site?
If so why don't you just add to that Web site?
I don't think you are going to find anyone here who will build you a "multiuser application."
Or at least they most likely wouldn't do it for free.
The purpose of forums such as this is to help people to learn and build their own Web sites or whatever.
You start out and do what you can do and then if your code doesn't work or you can't figure out a particular step, you post your code or question here and someone who knows the answer posts a reply.
You are going to have to do quite a bit of work to make a site like you are talking about work properly.
The file you posted the link to is a text file and therefore it won't be as easy to work with as say a database file would be. Also, there are not any clear separations of the information in the text file. By that I mean that none of the information is separated by commas or other punctuation and that makes it harder to break up into meaningful information.
For example:
DARK HORSE
OCT050046 BERSERK VOL 10 TP (MR) $13.95
NOV050048 BLADE OF THE IMMORTAL #109 (MR) $2.99
NOV050015 CONAN #24 (MR) $2.99
The only real break is after the date code on the left: OCT050046.
These date/numbers appear to all be different, so maybe you could use that as some sort of an index number.
I think the first thing I would do would be to copy the text file into Notepad.
Then I would write PHP code that would read the text file and put the date/number into a field and then the rest of the information into another field.
I would also try and separate out the price and put it into a separate field.
One problem there is that they don't all have prices, but you could work around that.
Then I would add a check-box as the first item on the left side of the screen.
When a user went to the site and request the comic book list, this form/list would be displayed. After the user entered a check into the text boxes beside the items they desired I would read the checked items into a database. A database would make it much easier to manipulate the information to do whatever you might want to do with it. Send it to Admin or whatever.
You could easily track which user was interested in which comic book and things like that.
There is a lot of work to be done to make a site like this work and work properly.
I am sure that no one who comes to this forum has code such as this just laying around waiting to be emailed to you.
I would suggest that you start by reading the PHP manual or a good PHP book about reading from a flat file. I think it would be quite easy to write PHP code that would take the text file from Notepad and read it into a form with check boxes beside the items.
Give it a try and see what you can come up with. Then, after you have some code, you can come back here and see if someone can't help you with any parts of your code that does not work.
Good Luck.