Well ill awnser myself.
To get working an atmega48 whit arduino ide, just add this board to Boards.txt in the arduino directory.
atmega48.name=Rotceh-hack QM7298 w/ ATmega48V xD
attiny48.upload.using=arduino
atmega48.upload.maximum_size=4094
atmega48.upload.speed=19200
atmega48.bootloader.low_fuses=0xE2
atmega48.bootloader.high_fuses=0xDF
atmega48.bootloader.extended_fuses=0xFF
atmega48.bootloader.path=atmega
atmega48.bootloader.file=atmega48.hex
atmega48.bootloader.unlock_bits=0x3F
atmega48.bootloader.lock_bits=0x0F
atmega48.build.mcu=atmega48
atmega48.build.f_cpu=8000000L
atmega48.build.core=arduino
atmega48.build.variant=standard
Source: http://forums.hackaday.com/viewtopic.php?f=2&t=2161
Then just compile ur scketch and upload it whit avrdude in command promp.
Or if u want upload it whit the arduino interfaz ull need to modifie the avrdude.conf file ( arduino-1.0.1\hardware\tools\avr\etc) and change the signature of the atmega48.