Another comment on this pet peeve of mine...
I have noticed that Banks and other Financial online systems seem to be the absolute *worst* about this - I have yet to find one that allows me to use a *strong* password - like you, I have found they *all* only allow letters and numbers - *very* insecure, from a password cracking point of view.
Please, *please* complain *loudly* to them, and *demand* that they allow the use of strong passwords - tell them you'll change to another bank that *does*, due to the recent number of break-ins and such that have been publicized recently - its no *wonder* they are getting broken into, if they only allow 6 (or 8) character passwords, and don't allow non alpha-numeric ascii characters...