I just reinstalled newest Debian squeeze Linux for my amd64 Linux laptop (old Fujitsu Siemens) Linux Kernel 2.6.32-5-amd64. After that WD MyPassport 500GB external hard drive mounts automatically and is readable but not writeable. I worked this problem thoroughly for one week(!), tried all complicated tricks with superuser terminal without success.
Then, almost by accident I managed to solve this problem, with a very easy way (!)!
Just install package “NTFS-3g” with Synaptic, just clicking it from that packet list! Too simple to be tru…I dont know why it was not installed by default?! After that WD MyPassport works perfectly.
-certainly there is different situations in different linux/hardware combinations but this was the problem and perfect solution in my case!
Hope that this helps someone other struggling with this problem