Script To Determine Who Visited Your Website

Hi All,
I thought Debora's question would solve my problem but it didn't, probably
because her problem is slightly different.
I have a catalogue on my site which I want to give other friendly retailers
access to, (perhaps for a fee) to use as their own catalogue within their
sites,  because we are all in the same trading group.
How can I make sure that only those that I give permission to use the
facility, have access other than using it as part of my site in the
conventional way?
I will be giving them the URL or script to use so can something be imbedded
in that URL to say who they are? If so how do I use it? Also is there a way
that I can send the surfer back to where they came from when they hit the
home button. (i.e. a variable URL)
I could do it by having a different catalogue set up for each of them but
that seems like a sledgehammer to crack a nut and has massive maintenance
problems. The catalogue will change five times a year to coincide with
brochures we all deliver as advertising.  The catalogue that is on the site
now has experimental ordering facilities but at first I will not offer that,
but when I do of course it will be even more important to find out who
generated the order so as to send the order and pay the money over to them.
Also does anybody know of a freeware program for sorting out capitals in
links, I have a nasty habit of occasionally doing it and although CuteFTP
sorts the file names out when uploading I need something to scan my code.
Thanks for any help you can give, please copy any replies to my email
address as I sometimes get a bit behind with reading the list.  Any comments
about the site (Good or Bad would be most welcome)
--
Regards,

Steve Robinson
Rye DIY Home Centre
e-mail: ryediy(at)iname.com
Web: http://www.ryediy.co.uk

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