Replacing atmega8 with atmega328(arduino)
I want to share my experience. You can use lots of different bootloaders with serial single sided board but you have to take care of two things:


You have to change serial port setting for its speed like if you are using decimila or NG bootloader it should be 19200 bits per sec. 
Select the correct board type in the Arduino IDE, which will depend on your boot loader.
You can find this information in the board.txt file, like speed of port, board name and fuse bit settings if you are loading the bootloader in a new, blank chip.


Hope this will solve your problems.