I tried manually copy the mediascape.apk to /data/app, reboot, then mediascape is restored in the application drawer and can be run functionally.
Here is the details.
Connect the X10 to PC using USB debug mode.
Get the adb.exe ready (you can run it from the root step4 folder directly)
0. Copy mediascape.apk to the step4 folder.
1. Start command prompt as administrater.
2. Change to the step4 folder.
3. Run "adb shell mount -o remount,rw -t yaffs2 /dev/block/mtdblock2 /system" without quotes.
4. Run "adb shell chmod 777 /data/app" without quotes.
5. Run "adb push mediascape.apk /data/app" no quotes.
6. Run "adb shell reboot" no quotes.
BTW: I have copied all the mediascape related files back to /system/app as well, by running "adb shell chmod 777 /system/app" and using adb push.
Seems it's not ideal as the apk is not installed but added to the X10 directly.
Any better ideas?