Software protection: Question on basic concepts

Ok, I made a software with embedded visual basic 3 for HP IPAQ PDA. My marine company wants me to make sure the software cannot be hacked easily. We are planning to sell the software together with the PDA, so the software can only run on a particular PDA with a particular serial number. :D

I have a couple of questions on software protection concepts :

1. Generally, I should create a file with some encryted numbers and put it with a folder with a obscure name and hide it somewhere in the registry of the PDA, correct? I should not hide the file in a folder that have my program name because hackers can easily find that file and copy the contents of the file, correct?

2. For (1), generally which is the best folder to put in the encryted numbers? I don't want to mess up the registry.

3. I feel really uneasy messing with the registry of my PDA; I have never done it before. I thought about putting 5 encryted password in 5 separate text file and hide them somewhere in 5 windows or programs folders. Good idea?

4. Do I need to scramble the evb3 code?

5. In HP IPAQ, it has a hpAssetViewer.exe that generates a hpAssetViewer.txt (inside contains the IPAQ serial number) every time the .exe is ran. I code my program to start the hpAssetViewer.exe, have it generate hpAssetViewer.txt and then my program will read the serial number inside hpAssetViewer.txt. The only problem I am concern about is some hacker may delete hpAssetViewer.exe and create a simple program of their own that can generate text file with the IPAQ's serial number and name it hpAssetViewer.txt. I haven't tested this theory yet; I am afraid to do it because I am not sure what will actually happen if I delete the hpAssetViewer.exe, maybe my IPAQ OS will be cripped or something. :eek:

6. Is this all there is to software protection? :D

7. Any good links for me to understand the basic concept?

Thanks