If you have a robust operating system which will allow a process to allocate a private area of memory and place security controls on it so that no other process can read it even if the process is spawned by the same user, then you are safe from memory scanning. Unless your smart user forces a crash and preserves a swap file with the information in it of course.

If your operating system won't allow this then the memory (including RAM drives) can be read, and possibly changed.

The other problem is, if I can read the program I can take a copy to another computer which I have complete control over and fiddle to my heart's content.

A quick search at www.download.com gave me WinHack and MemoryBrowser, both of which will allow you to browse your local PC memory and RamDump which will dump the contents so you can play with it off-line.

Of course you need to be quite a sophisticated user to think about cracking the encryption that way, or using a debugger to step through the code and interrogate internal buffers.

You need to decide whether you simply want to deter accidental disclosure of passwords and the script code, or if you need a highly secure solution.