It's not possible to decrypt md5 and sha1, they only encode.
Um, hello, just store the word and its hash, then you can look up a hash and get its word.
Or loop through every letter/word combination to find the hash that matches the word it's currently looking through.
Also, a really tricky conversion to do is:
However, encrypting like this is not very easy.
a = original password
md5(md5(sha1(md5(a))))
And you can really take it further by converting a character to a different character each time.