from what the community has gathered, the n100 is a cut-down version of the OSD. Neuros wrote the customised for Emtec, writing some closed-source apps for their needs. I've never seen or used one, so I don't know much.
1. It's year 2011 (EMTEC n100 released in 2007/2008). Is there any upgrade (firmware, anything...) avaible for this device?
Not that I know of, no.
2. Someone heard any news about programing/changeing something on EMTEC n100 by Neuros group or freelancers?
A little, but not much. I had a quick look at the firmware file to see if I could open it up and hack around, but it appears very different to the OSD's firmware files. It may be obfuscated or encrypted.
I myself did a little freelancing customising the OSD firmware for surveillance tasks. But the n100 is an unknown quantity to me.
3. Does EMTEC n100 support overwritting file when disk space ends? (I don't want to end recording after space end)
Probably not, as the OSD doesn't do it by default (see below).
4. If it doesn't support overwritting after end of space IS THERE ANY GOOD HEART MAN WHO COULD EDIT FIRMWARE AND ADD SUCH OPTION?
Well if someone could figure out how how the firmware is being protected, then it would be possible to change the open-source code.
5. Did anyone use this gadget as surveillance device (with composite cinch camera)?
I'm gathering this is your intention. The OSD has been used as surveillance recording device by various people. It can be easily scripted to enable a sort of auto-overwrite.
6. Does it support 1TB HDD's?
Yes. Preferably using FAT32.
I wish you luck!