Secure server solutions for clients

Hi there,

I am a looking to work for a few people in different countries and am looking for a secure and cheap way for them to upload their projects so I can work on it on my mac and then post the completed work for them to download.

At any one time, there may be a few small projects in progress and it is really important that each client has their own log-in and can view only their data. Each project will probably be a max of 2Gb.

I use a Mac and but am not too clued up on the type of solutions available... do I have to have a third party to provide this service such as Yousendit etc (any ideas who is best?) or can I do it myself on my mac by simply setting up an FTP server linking to a particular secure folder or something??

I will shortly be upgrading to Snow Leopard from 10.4.11. Any help or suggestions greatly appreciated! Thanks.