This is how i did it:
1. I took out the harddisk of the NWSP2 casing.
2. Connected it through a Sata to USB interface (in Windows)
3. Used a Ext reader for windows (http://www.diskinternals.com/linux-reader/) to get access to the files on the disk under windows
The main reason I was doing the above steps where to save my data, put the drive in a USB enclosure and format it under windows so I would get a normal external USB disk. But after copying my data I was curious about the other partitions on the HD. Then, while exploring partitions and files I found the "host" file in de Linux1 partition.
When I viewed the content of the host file, it listed the IP adress of the NWSP2!!!!
But is was an IP address in a different IP range as I use now for my internal network. Present IP range is 192.168.137.x and the IP in the host file was 192.168.1.x
In order to login (with 192.168.1.x) I connected the NWSP2 directly to a laptop (with no internet access) and typed in 192.168.1.x
And (amazingly) it asked inlogname and password. Then, like I stated I didn't use the admin-nas inlogname and got only a part of the web interface. After logging on with admin-nas and password, I got the full web interface.
Because I'm on 192.168.137.x now, the first thing I did was going to the LAN settings and typed in a 192.168.137.x IP adress.
Then, disconnecting the NWSP2 from the laptop and connecting it to my current network / switch (and powering on again) I goto 192.168.137.x and: tada: the full webinterface is available. (At last..... hehe) :-D
And now: I'm on firmware 16 !!!!!!!