Text file compression (Score 1)

I've thought of this before, but it has always seemed unachievable, (still does.) It would sure take a while, but I bet you could compress a text file quite a ways more than gzip if you took a sample piece of text from the beginning of the plaintext and appended it to the hash, giving a hint at what the plaintext message would be, (narrowing the number of possible plaintexts the md5 would decode to.) How would it be to compress an encyclopedia to an md5 hash and it's first paragraph or two? Getting it back would take a while :)