Tilly's advice is very true -- some other programming community websites that I visit have "encryption" code sections. Most code offerings have one of three themes.

• Code that produces a cyphered text, takes negligible time to brute force.
• Code that produces a cyphered text, takes negligible time to brute force, won't decrypt own cypher.
• Caesar cyphers.

If you feel the need to try your hand at encryption, try one of the better documented, free (speech) algorithms : blowfish. Source code (in C and visual basic) is present, as well as a white paper describing the algoritm. There's even a set of test data to verify your implementation's correctness.

Again, writing good encryption is sticky stuff -- especially when TASMWTODI, including blowfish (and even an all-perl version). So, unless you have a wild encryption itch to scratch, I'd suggest one of these existing modules.
update : Level II encryption??? what's level I? ;-)