That's odd. Are you using a Mac or Linux? It worked without a login required for both of my computers that were using Windows.
My guess is this works like "anonymous ftp" in which you can just type "anonymous", without the quotation marks, for the userid and anything at all for the password:

Anonymous FTP: Frequently Asked Questions (FAQ) List.
"Anonymous FTP is a facility offered by many machines on the
Internet. This permits you to log in with the user name 'anonymous'
or the user name 'ftp'. When prompted for a password, type your e-mail
address -- it's not necessary, but it's a courtesy for those
sites that like to know who is making use of their facility. Be
courteous. Some sites require a valid e-mail address, others don't."
http://www.faqs.org/faqs/ftp-list/faq/

It should also work to download the full 500 mbyte image and use he IAS viewer to work on that. Since the full image doesn't have to be open all at once with the IAS viewer this shold still work with systems with low amounts of RAM.

Bob Clark