[Q] Please help me mount RW

Hy my friends.
My name is Chris,from Romania.
First ,please excuse me for my poor english !
I have a Prestigio Multipad PMP5100C tablet.I flash it with a rooted firmware ,by arktablet.com (Arnova10 custom firmware,Android 2.2.1,froyo). It work good

for me,but I can not access system file,because is mount Read-Only.
I try "mount -o rw,remount -t yaffs2 /dev/block/mtdblock3 /system" ,but not work.
With adb I got this :


Microsoft Windows XP [Version 5.1.2600]
(C) Copyright 1985-2001 Microsoft Corp.

D:\Documents and Settings\Administrator>g:

G:\>cd G:\SDK\sdk\platform-tools

G:\SDK\sdk\platform-tools>adb devices
List of devices attached
11223344 device


G:\SDK\sdk\platform-tools>adb shell
# su
su
# cat /proc/mounts
cat /proc/mounts
rootfs / rootfs rw 0 0
/dev/root / cramfs ro 0 0
tmpfs /dev tmpfs rw,mode=755 0 0
devpts /dev/pts devpts rw,mode=600 0 0
proc /proc proc rw 0 0
sysfs /sys sysfs rw 0 0
none /proc/bus/usb usbfs rw 0 0
/dev/block/mtdblock4 /system cramfs ro 0 0
/dev/block/mtdblock7 /data ext3 rw,nosuid,nodev,errors=continue,data=ordered 0 0
/dev/block/mtdblock6 /cache ext3 rw,nosuid,nodev,errors=continue,data=ordered 0 0
/dev/block/mtdblock9 /data/data ext3 rw,nosuid,nodev,errors=continue,data=ordered 0 0
tmpfs /mnt tmpfs rw,mode=755,gid=1000 0 0
tmpfs /mnt/asec tmpfs rw,mode=755,gid=1000 0 0
/dev/block/vold/31:8 /mnt/sdcard vfat
rw,dirsync,nosuid,nodev,noexec,uid=1000,gid=1015,f mask=0002,dmask=0002,codepage=cp437,iocharset=iso8 859-1,shortname=mixed,utf8 0 0
/dev/block/vold/31:8 /mnt/secure/asec vfat
rw,dirsync,nosuid,nodev,noexec,uid=1000,gid=1015,f mask=0002,dmask=0002,codepage=cp437,iocharset=iso8 859-1,shortname=mixed,utf8 0 0
tmpfs /mnt/sdcard/.android_secure tmpfs ro,size=0k,mode=000 0 0
/dev/block/vold/179:1 /mnt/sdcard/external_sd vfat

rw,dirsync,nosuid,nodev,noexec,uid=1000,gid=1015,f mask=0002,dmask=0002,codepage=cp437,iocharset=iso8 859-1,shortname=mixed,utf8 0 0
# exit
exit

Please help me to mount my device as RW.
Thanks in advance.