Can I use something like this http://translate.googleusercontent.com/translate_c?act=url&hl=pl&ie=UTF8&prev=_t&rurl=translate.google.pl&sl=pl&tl=en&u=http://allegro.pl/konwerter-ft232-usb-rs232-ttl-interfejs-ft232rl-mi-i1813924104.html&usg=ALkJrhh29pOuBx5lwONzJnWNtlRT_inoXA (sorry for translation...) to burn bootloader and upload sketches to arduino compatible boards ?
It's difficult to tell (and not just because of the translation.)
It is NOT useful for burning the bootloader; that would require additional pins.
For uploading sketches, it depends on whether the "compatible" board has an actual "rs232" interface or just an "5V logic ("TTL") serial interface", and which version this adapter actually supports. "Real rs232" has +/-5V (or more) and is inverted compared to the 0/5V logic of "TTL serial"; they won't talk to each other.
Can I use something like this ............. to burn bootloader and upload sketches to arduino compatible boards ?
Quite simply no.
Can Anyone answer: WHY not?
I'm sure a whole bunch of people would like to know. Thanks.
For bootloader, you need to control MISO, MOSI, SCK, Reset, and have Power & Gnd.
Having Rx, Tx, Gnd leaves you a few control signals short.
Insert Quote
Can Anyone answer: WHY not?
Because it only provides the serial signals. To program in a boot loader you need to use in effect the SPI interface. This consists of clock and data signals that are synchronised. Normal serial data is asynchronous communication which is a different format. If you want to know what you need to do, that is what lines to waggle then look at the ATmega's data sheet, that will tell you.
It's like saying why can't I fly in my car, it has an engine like a plane. It is because they are both designed for totally different things.
Ok I See difference 
So to burn bootlader I need stk500 or for Ubasp (for example)
Or in fact an arduino can be programmed to act as a boot loader blower for another chip.
It's like saying why can't I fly in my car, it has an engine like a plane. It is because they are both designed for totally different things.
Understood; and at least You made me smile. Wish everybody would!
I tried to use my UNO as programmer... but optiboot doesn't support ISP
I tried to use my UNO as programmer... but optiboot doesn't support ISP
It does. You will need to use a capacitor (RESET to GND) instead of a resistor (RESET to 5V) to disable auto-reset.
Tried this but there is small problem - http://arduino.cc/en/Tutorial/ArduinoISP
NOTE: Currently, you cannot use an Arduino Uno as an ISP programmer because the optiboot bootloader does not support this sketch. A revision for this is in progress.
That note is wrong.
Ok I tried to use arduino as ISP (using 10 uF cap to disable autoreset ). So far I have one problem - bootloader is burn properly, blink sketch is burn properly but when I try to upload new sketch something happens and second arduino is bricked till next bootloader burning... and same still.
Maybe I need to burn new version of optiboot on ISP-arduino ? I bought it year ago... maybe little update will help ?
bootloader is burn properly
Are you installing the bootloader using the IDE or from the command line?
Maybe I need to burn new version of optiboot on ISP-arduino ?
The latest version of optiboot...
http://arduino.cc/forum/index.php/topic,64105.0.html
...works very nicely with the Arduino ISP sketch. With that bootloader you do not need to disable auto-reset.
I'm using IDE.
To update bootolader I need working ISP so I must visit my friend with one
After that I try to use UNO as ISP to burnt bootloader on atmega8 based circuit and leave note.
one problem - bootloader is burn properly, blink sketch is burn properly but when I try to upload new sketch something happens and second arduino is bricked till next bootloader burning.
This could be the result of incorrect fuse settings. If you fail to enable the bootloader section, the Arduino will start at flash location zero instead of at the start of the bootloader. When the chip is otherwise blank, location zero through "start of bootloader" contain an irrelevant instruction, and the bootloader will eventually start and appear to run normally. After you've downloader a sketch, though, you'll have "real code" between zero and the bootloader, and the bootloader won't get control.
So IDE settings are bad ? I don't used external software to set fuse... but today I might try to use it. I fount settings :
lockbit65 set to 10
F8 fusebit set to RS - 1024 words Q- 0
So I uploaded hex file from optiboot thread, (used hex file from attachment,verified,I don't touch fusebits or lockbits used avrdude with procedure erase-write-verify ) and another problem appears. Board have no communication with PC.
For now it not respond to being plugged to USB port.... So must be problem with code ?
What now ? Use IDE and ubasp to upload data once more ?
Previously you referenced an ATmega8 board and an Arduino Uno. Which of the two boards have no communication?