I need to host some files, but not sure which way I'd want to do it.

I could give up anonymous access to everyone, but that way I wish I could restrict each anonymous to dl using one connection at a time, meaning they cant open 10 lines using flashget to download one file, or download multiple files at the same time with 1 IP.

Another way however, I could set up a username and password and post at my site and let everyone use that account, but I would also like to restrict each IP download only one file at the same time and using one connection at the same time.

I have searched over proftpd directives, and I can only seem to find .maxclientsperuser that could work, but not very what I want. Can someone tell me how can I achieve the restriction above? I am running Linux, proftpd.

MaxClientsPerHost would do the same thing given that each anonymous user has its unique IP address/Hostname.

Um...what about for non-anonymous users? Can multiple people share one user account but download using one connection at a time?

Yes. No matter how many accounts they are sharing, MaxClientsPerHost can limit one user per connection. :)

Cool, but that applies to the whole server, including the owner. Would it be possible to grant more connections to a particular users??

You can set different limit in each of the virtual host. I don't think you can restrict the number of connections to a specific user.