Assistance Cracking Classical Cipher
I don't know the solution, but since you say you're only asking for hints, here's a few that occurred to me:


If this is a Vigenère cipher, the missing character at the beginning should not matter (much): if you encrypt a message with the key FOOBAR and drop the first letter of the output, you can decrypt the resulting ciphertext with the key OOBARF.
As ewanm89 notes, the obvious way to attack a Vigenère cipher, after you've determined the key length is $n$, is to write it with $n$ letters per row and attack each column as if it were a Caesar cipher.  There are automated tools for doing that, such as pygenere; they may not always give the correct answer for very short messages, but yours looks long enough that they should at least have a decent chance.
The most notable feature I see in your ciphertext is that the string HIMFTF occurs twice, at offsets 26 and 86.  That does strongly suggest that the key length may be a divisor of 60; alas, 60 has lots of small divisors (including 6, which you believe the key length to be), so that doesn't really give that much information.  It does at least rule out 7, 8 and 9 as likely key lengths.