Visual Basic Question

Of course. You just need to write your own custom file format, language doesn't matter.

The simplest way of doing this would be to insert a boolean variable in a file; if it's true, it means password protected. When you read the file, check if this boolean is true. If so, pops out a dialogbox, ask for a password, then compare it to the password inside the file.

First ask for a password,

like,
inp = inputbox("What is the password?")

You then turn int into a number,

i = 1
for x = 1 to len(inp)
i = i * asc(mid(Inp, x, 1))
i = (i mod 256) + 1
next x
i = i - 1

You then open the file for binary as #1 and dump the contents into a byte-buffer

dim bytebuff() as byte
open filename for binary as #1
redim bytebuff(lof(1))
get #1, , bytebuff
close #1

You then decrypt it,

for x = 0 to ubound(bytebuff)
bytebuff(x) = bytebuff(x) xor i
next x

And place it back in the encrypted/decrypted file
open decryptedfilename for binary as #1
put #1, , bytebuff
close #1

and your done!
(WARNING NOT VERY SAFE, KEEP OUT OF REACH OF SMALL CHILDREN)
DENC