Hmm, interesting anomaly, but irrelevant to be honest.
Why have you installed "the three other versions" and are trying to "install" EotN? The latter requires no installation, just the addition of the serial key to your existing account.
first i installed guildwars, then gw factions, then gw nightfall and finally i wanted to install eye of the north to avoid downloading it cause i'm low on bandwidth
and why did they provide a dvd with EotN of you only need to add a serial?
I don't have an EotN DVD to hand (I bought mine via the ingame store) - but I would expect that, if you explore the contents, you will find a gw.dat somewhere. That's all you'll need.
All the game dvds have the same information on them so a multiple install doesn't save any time.
Install from the NF disk and then let it update anything that's needed.
Then use a memory stick or a dvd rw disk to store the game files for any future calamity.
You can update those files say a couple of times a year and your all set for a reinstall.
Copying the files to a new pc and running the exe file will install the game set up folders and short cuts without ever having to touch the game disks ever again.