I even built a level adapter with 2 transistors, based on the Arduino S3v3 Revision 2 schematic that like Diavolino outputs directly RXd, TXd and Reset.

I then connected Diavolino to normal RS-232c on COM1 (XP).

It does work and I can upload sketches.

But  I get the avrdude:stk500_disable():protocol error, expect=0x14, resp=0x00   OR 

                    avrdude:stk500_getsync():not in nsync:resp=0x00