Two options come to mind, BestCrypt and WinRar.
BestCrypt uses the BlowFish Algorythim, VERY VERY VEEERRRYYY hard to decrypt. More than likely not decryptable.
2nd, use WinRAR, create a RAR archive, compress is with the "Store" option, with a password including letters (both cases), numbers, and symbols at least 8 characters. Even the best RAR cracking utilities will have an extremely hard time decrypting a RAR file that does not use compression (store). To be able to hack such a file, you can only use the brute-force method; brute force'ing a RAR will take FOREVER, literally. The way that the new WinRAR makes the archive, the cracking utilities can only check 100-300 brute force attempts per second. If you make your password >8 char, up/low case, numbers, and special characters, you're looking at (26x26x10x16)^8 or over 1.87^40th.
At 300 brute-force attemps per sec, you're looking at 1.29^32 years.
-SF