OS X :: ITunes Data Missing/deleted And Access Rights On Mac?

Having a bit more time, i stuffed up my iTunes library and can't fix it and would really appreciate any kind of advice.

A few things reg my mac and myself before I come to the core of the problem:

I have a macbook air, no 'extras' inside (normal 1.6GHz) and it's running at home with an airport and an external HDD of a few gig to store my data and backups. OS is Mac OS X 10.6.2 (10C540).

I am not a mac specialist and just started using mac roughly over a year ago and never got the real 'cores' but bit by bit I get there (I thought ).

And just btw I am not an english native speaker so I may phrase things 'funny' from time to time

I have my music, videos etc on my ext HDD and a copy of music on my mac as I like to have it with me 'on the road'.

As I was the only user it was just in my 'Music' folder

My bf just moved in and is wrapped by the mac anyway and had a user for a while. With his new iphone I *wanted* to copy the music to Users/Shared so we both can have it in our iTunes

This proofed to be not that easy as I couldn't give him access rights even though the music was in this 'shared' folder. With the 'information' of each folder I tried to give him access rights (rea & write) but even by doing so for some folders and their sub-folders, I still can't import these files into his library.
So there are my first (hopefully quite basic questions)

How can I give him access to all these music folders so he can load them into his iTunes? As I would like to prevent to click each folder and sub-folder - is there a way to speed this up?

Standing for this problems and having messed up my music a bit as the links of my itunes weren't updated to the new music location, I somehow (stupid stupid stupid) tried to make it work without making any backups of my library files and without having any in-dept knowledge about iTunes and how it actually works/ stores its information etc.

To cut a long story short: my whole iTunes it totally 'empty' : no movies, music, even iphone apps are there anymore and even when I connect my iphone nothing happens. I have no backup what-so-ever and unfortunately can't give you the steps I went to mess it up that way because I just panicked along the way and didn't trace my steps or stopped at the right moment to look up some handy and useful manuals/ guides. Would love to explain an interesting and maybe challenging error for you guys but that's the boring truth.

I was wondering if it makes sense if I de-intall iTunes now completely and then re-install it and import the music/ movies into both users iTunes and make a clean set up. As it is Christmas time I have a bit of time and this wouldn't bother me too much. So the question is here: would you recommend this / agree? Are there any tipps you would give me/ things to do to make this work?
And this of course still leave me with my access rights problems as all the music folders are under "shared" and my bf's account somehow doesn't have access to it. I have still a backup of that data on my ext HDD so I could delete it on my notebook and re-copy it to somewhere if I know where/ how to make it work.

Hope this is not too messy for you all to read through! I would really appreciate if I would get some hints/ tipps/ advice from you.

Oh something I forgot: before I wrote here I searched this forum and some others as well the apple standard help and tried to 're-create' my library but as deleted my rubbish bin within my mess-up-process I think I deleted the original files.

I think part of the whole problem is the missing back up and of course my half-knowledge of mac/ iTunes.