ie7 compatible password procedure

Oh dear, oh dear!

I am a secondary school teacher. I run a website as a hobby.
I also use this site to cummunicate information to my students (schedules,
keys, results, etc.).
In order to protect my students'privacy I have used a password procedure.
However, today one of my brighter students drew my attention to the fact
that this javascriptprocedure is incompatible with the new IE-7.

Sad times.

Is there anyone who knows of an IE-7 compatible password script I could use
instead of the old one?

I will greatly appreciate your suggestions!

Nico