The downloads site is still trying to recover downloads and put together packs, so the site doesn't allow signin's and registration to anyone yet. But it will be up and running soon like it used to be again, I hope. Guess you'll just have to wait until then. Here's a link to more info about it from all the staff at Zoo Admin. Hope this Helps!
Link To Info: http://www.zooadmin.net/index.php?topic=378.msg3690#msg3690
(Called Re: Important Announcements From the Webmaster/Second From Top)
:)) clap :)) clap :)) clap :)) clap :)) clap
PS: I know it says it's for Zoo Tycoon 2 on the info, but it goes for Zoo Tycoon as well because they both share the same downloads site. Just for clarification for you.