I retract the statment that 150GB should not be a problem. The max size of a FAT32 partition can be 2TB. However, I remember others having a similar problem with large FAT32 partitions. What kernel are you running?

i think i'm using the bare.i kernel

Maybe it's a ntfs file system,

try

also you can try

This is what i get when i try

mount -t auto /dev/hdb5 /mnt/d
or
mount -t ntfs /dev/hdb5 /mnt/d

mount: wrong fs type, bad option, bad superblock on /dev/hdb5,
missing codepage or other error
In some cases useful info is found in syslog - try
dmesg | tail or so

and this is what i got after dmesg | tail

i810_rng: RNG not detected
hw_random: RNG not detected
pci_hotplug: PCI Hot Plug PCI Core version: 0.5
shpchp: shpc_init : shpc_cap_offset == 0
shpchp: shpc_init : shpc_cap_offset == 0
shpchp: Standard Hot Plug PCI Controller Driver version: 0.4
pci_hotplug: PCI Hot Plug PCI Core version: 0.5
pciehp: PCI Express Hot Plug Controller Driver version: 0.5
NTFS driver v1.1.22 [Flags: R/O MODULE]
VFS: Can't find a valid FAT filesystem on dev 03:45.

my hdb5 is not listed in /etc/fstab so i tried to add this line
/dev/hdb5 /mnt/d vfat defaults 0 0
and try mount /dev/hdb5 /mnt/d
still i have the same error line

I have seen threads where others have had problems mounting a large vfat partition. When it was resized to approx 125GB it could be mounted successfully. I don't remember the kernel version but there used to be a bug many moons ago.

well then, does that means i have to compile a different kernel?
right now i have 2.4.31

Well, 2.4.32 is out, but in the changelog I can't find anything related to (V)FAT filesystems, you can always try it, tho'.

Or you can try the lastest 2.6.15; Now that Linus has said that new-features can only be merged after 2 weeks of a new kernel release, I expect this kernel to be pretty stable -and that also means that sooner than later Pat will switch to 2.6, too.

My guess is, yes, you should try a newer Kernel.