Hi to all!
Thanks to Coray for the suggestion and for his linux.bin image:
I tried it and works for itself, but now i have problems with my server PC, not with linux image. Infact as shown in the output below, target linux cannot mount /tftpboot/ltib because the server returned error (-13 it says). 
The nfs server was configurated and restarted as sad in the user's guide.
I looked in my /dev directory but i didn't find any nfs device, so i thought that it could be the problem. Isn't it? 
If so, how could i solve it?
As you request me by mail i show you also the colilo "?" output
now it works correctly and my beginning problem was a bit stupid: i didn't know that colilo works by default at 19200 baud rate, while my coldfire and minicom was setted for 115200! 
So I seen garbage when i tried to run colilo!!!
Another thing: where can i found documentation that explain the rules for set colilo and colilo kernel command line? 
Thanks and regards,
Gianluca Salvador
colilo>?
Coldfire Linux Loader
 Platform: -- Colilo M547X - M548X Bootloader --
 -- 2005 Freescale/2004 Motorola(c) --
Commands available:
 b - boot default image
 m [addr] - memory dump at addr
 g [xfer_addr] - go to xfer_addr
 l [down_addr] [port] - load image from port
 f [down_addr] [size] [val] - fill memory with value
 pl [addr] [val] - set the 32 bit value at address
 ps [addr] [val] - set the 16 bit value at address
 pc [addr] [val] - set the 8 bit value at address
 rl [addr] - read a 32 bit value at address
 rs [addr] - read a 16 bit value at address
 rc [addr] - read a 8 bit value at address
 c [source_addr] [dest_addr] [size] - copy memory
 d [source_addr] [dest_addr] [size] - decompress image
 x [down_addr] [dest_addr] [xfer_addr] [port] - cmds l, d, g
 z [source_addr] [dest_addr] [xfer_addr] - cmds d, g
TCP/IP commands:
 set mac [MAC address] - set board MAC address
 set ip [IP address] - set board IP address
 set gw [IP address] - set board gateway address
 set netmask [IP address] - set board netmask
 set server [IP address] - set address of TFTP server for TFTP download
 set image [Image name] - set name of image for downloading
 set fec [fec number] - select FEC to use
 set cl [command_line] - set kernel command line
 set kfl [0/1] - set to 1 if kernel image is in flash, 0 - otherwise
 tftp [down_addr] - download image from TFTP server
 bootp - request bootp information
 Where:
 flash_addr - address in flash to start burning from
 xfer_addr: hex address to start running at
 down_addr: hex address of downloaded image
 dest_addr: hex address of image destination
 source_addr: hex address of compressed image
 size: size of compressed image
 port: 0 = /dev/ttyS0, 1 = /dev/ttyS1
 IP address: IP address in format xxx.xxx.xxx.xxx
 MAC address: MAC address in format xx:xx:xx:xx:xx:xx
 Image name: string, filename
 fec number: 0 or 1
 Default values for paramaters:
 down_addr: 1000
 source_addr: 7fc10000
 dest_addr: 1000
 xfer_addr: 2000
 flash_addr: 0
 size: 130000
 downloadPort: 1
 kernel command line: root=/dev/ram
 kernel image in flash: no
 start booting automaticaly: no
 Current TCP/IP configuration:
 Board MAC: 00:04:9f:b5:69:3a
 Board IP: 192.168.1.40
 Netmask: 255.255.255.0
 Board gateway: 192.168.10.1
 TFTP server: 192.168.1.39
 Image name: linux.bin
colilo>
colilo>g 2000
Linux version 2.6.10 (coray@fastball) (gcc version 3.4.0) #3 Thu Jul 6 16:48:26 CDT 2006
starting up linux rev 0.2: startmem 0xc0270000, size 61MB
Built 1 zonelists
Kernel command line: mac0=00:04:9f:b5:69:3a noinitrd root=/dev/nfs rw nfsroot=192.168.1.39:/tftpboot/ltib ip=192.168.1.40:192.168.1.39:192.168.1.1:255.255.255.0:ColdFire:eth0

f
f
PID hash table entries: 512 (order: 9, 8192 bytes)
RTC driver is not initialized yet, returning 1970.
Console: colour dummy device 80x25
Dentry cache hash table entries: 16384 (order: 3, 65536 bytes)
Inode-cache hash table entries: 8192 (order: 2, 32768 bytes)
Memory: 62528k/65536k available (1800k kernel code, 1016k data, 96k init)
Mount-cache hash table entries: 1024 (order: 0, 8192 bytes)
NET: Registered protocol family 16
Linux/m68k PCI BIOS32 revision 0.05
ColdFire PCI Host Bridge (Rev. 0) detected
PCI: Probing PCI hardware
SCSI subsystem initialized
Initialize Multi-channel DMA API Alpha v0.3 (2004-04-26)
Initializing Cryptographic API
rtc: RV5C387 RTC driver successfully loaded
MCF547x/8x DSPI device driver installed
Coldfire DSPI driver is loaded
ISA-Philips-Basic-CAN memory mapped CAN Driver 3.1_ColdFire_FlexCAN (c) Jul 6 2006 16:22:57
ColdFire internal UART serial driver version 1.00
ttyS0 at 0xe0008600 (irq = 99) is a builtin ColdFire UART
ttyS1 at 0xe0008700 (irq = 98) is a builtin ColdFire UART
ttyS2 at 0xe0008800 (irq = 97) is a builtin ColdFire UART
ttyS3 at 0xe0008900 (irq = 96) is a builtin ColdFire UART
io scheduler noop registered
io scheduler anticipatory registered
io scheduler deadline registered
io scheduler cfq registered
RAMDISK driver initialized: 16 RAM disks of 8192K size 1024 blocksize
ColdFire internal FEC driver version 0.11
Loaded prism54 driver, version 1.2
i2c /dev entries driver
i2c-algo-mcf.o: I2C ColdFire algorithm module is loaded.
NET: Registered protocol family 2
IP: routing cache hash table of 1024 buckets, 8Kbytes
TCP: Hash tables configured (established 8192 bind 16384)
Initializing IPsec netlink socket
NET: Registered protocol family 1
NET: Registered protocol family 17
NET: Registered protocol family 15
IP-Config: Complete:
 device=eth0, addr=192.168.1.40, mask=255.255.255.0, gw=192.168.1.1,
 host=ColdFire, domain=, nis-domain=(none),
 bootserver=192.168.1.39, rootserver=192.168.1.39, rootpath=
Looking up port of RPC 100003/2 on 192.168.1.39
Looking up port of RPC 100005/1 on 192.168.1.39
Root-NFS: Server returned error -13 while mounting /tftpboot/ltib
VFS: Unable to mount root fs via NFS, trying floppy.
VFS: Cannot open root device "nfs" or unknown-block(2,0)
Please append a correct "root=" boot option
Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(2,0)