Securing Memory Card? What should I do so that the Memory card in my phone works only in my phone? Also, I should be able to connect my mobile to a PC through a USB cable and completely see/edit/organize the data on my memory card.

I want this to prevent anyone from gaining physical asses to my mobile, removing the memory card and getting asses to my sensitive data, by using the memory card with some other device.
You could use encryption on the entire drive. This can be done with certain apps like EDS (which creates an encrypted container on the device, which requires a password to be opened -- but after that the file system is mounted transparently for all apps to access; these containers are TrueCrypt compatible). Some of these Apps (like e.g. Cryptonite or LUKS Manager) require the device to be rooted.

However, if those encryption does not work on the device filesystem itself (but uses containers), I'm not sure how an app will work with it if it expects files at hard-coded places. You can try and find out, as most of the encryption apps offer free trial versions.