Basic ??? question?

Hi folks,
Maybe I’m getting old... but it always frustrates me the PC world, where difficult things are made so easy… whereas things that should be easy to explain become “obscure holes” nobody dares to dig in!
I’ve done quite a number of ADSL installations, different ISPs, different HW, different routers.I usually install one first PC, via RJ45 cable, one second PC wireless (WIFI).But so far I never had to install a third or fourth PC. Well, some day had to be the first time!

Today I had some problems, and trying to analize them, called up technical support of our ISP just to end up having a big and fustrating discussion.
I see different questions. Forgive me if some of them seem stupid, but when I don’t know something… just escalate it to find the answer, and this was no the case!

All routers I’ve seen so far, when you configure them for security, say WEP type, will ask you 64 or 128 bits? Character or Hexa? Those are clear.
But then, when you enter the key (usually, it’s pre-assigned by the ISP in the router itself, in its bottom) you can type it up 4 times for KeyIndex =1, 2, 3, 4
(Maybe they could even be different, but that I never tried)

The MAIN problem down I think relates to the meaning of what is called "KeyIndex".
The problem is I had my first WIFI configured, default is KeyIndex 1, and worked OK.
Did the same for a second PC, exactly equal, and got an error : duplicate names in the network??? (By the way, PC-Ids are different!)

Of course, they both had WinXP Professional SP2 (plus lots of other fixes), DHCP enabled, IP address automatic, DNS automatic, … etc

I thought one could have MANY (not thousands, of course, because of performance, but 5 or 8, maybe?, up to 10?, PCs WIFI connected to the same network)

Questions:

1- What is the “meaning” of that “secret word” KeyIndex? I searched Google, but found tons of info about basics and advanced configurations… but no one dignified to get down to explain basic things like this!

2- If I have to give each PC configured for my network a different KeyIndex… does that mean one can only have up to 4 WIFI PC’s connected at a time?
Same question but reversed: How many WIFI PC’s can coexist (regardless performance) in the same network?

3- My technical suppoprt ended up saying KeyIndex was none of the parameters asked for WIFI !!! even though I was telling him “I have it in front of me”!!! and suggested me to
- Eliminate any use of DHCP!
- Hard configre an IP address for each PC (?)
- Same for DNS
- … absolutely nonsense!

Or… am I absolutely wrong?
TIA
Sorry for this lengthy mail