Bluetooth developer kit for NXT.

I am trying to write a program that connects to a NXT and does some stuff like changing the name, reading and writing files etc.
Problem is I work on linux and use C and there is very little info around on that.
I got the Bluetooth Developer Kit from LEGO that gives some info on the command cods to send to the NXT to achive some tasks but I hit a snag.
I was able to open a connection (Bluetooth), talk with the NXT and send some commands. Up to now I have a prog that can: - Get Info from the NXT (NAME, BT address, battery level..) - Change the name - List all the files - Delete a file - Run a Program - Stop a program running
I am working on the writing of files and nothing works (almost). First of all the BDK has 3 different OPEN WRITE command and no hint what the difference is between OPEN_WRITE,OPEN_WRITE_LINEAR and OPEN_WRITE_DATA. Then it seems that none of the 3 works at least following the info... I had limited success but only for very short files and only if I don't use the extensions recognized by the NXT(?!).
Does anyone has more info on this or knows exactly how to do that? I looked around but all the source code I found that does that is in some strange(for me) language and from what I can see the method seems the same I use but maybe there is something more that I miss.
Any help?
Thanks, G
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