Multiple users on a Mac Mini?

I am starting a business that will require registration and cash exchange. There will only be one program that will be used in this process but my question is can such a thing be done using a Mac Mini, because I will need multiple users at the front desk and and a small sign in table for 1st time customers. After the first sign in their names and other info will be kept on file. I know that the program I need will probably require a windows platform but that can be dealt with later. I am just wondering if multiple users on 1 Mac Mini is possible and if so how many at once?

Do you mean that it will be used as a server with multiple people accessing it simultaneously or will it be one user at a time with different users throughout the day?

it would be Multiple users, Simultaneously

There is some geeky command line stuff you could do with exporting displays to other computers so many people can simultaneously be logged into multiple discreet desktops served up by one computer at the same time. I doubt it would be practical for business use and doesn't sound like what you need. It sounds like you need multiple open (read only or read/write?) sessions to an application hosted by one server. You may want to see if there is some software or database out there that does this. Mac OS X Server might be an option for multiple desktops, but I don't have any practical experience with it and I'm not sure it would help with multiple concurrent session access to data anyhow.