beginner questions

Hi Everyone,

I am new at this and I need some help,
I am the new system admin for a Internet company

Most of our bandwidth is use and we don't really know why.
After researching the internet looks like Netflow technology would be a good way to know where my bandwidth is going.

I just want to know what do i have to do to be able to use this technology.

Do I need some kind of hardware?
Can I just use the free tool or do I have to pay?
Can I install Netflow analyser anywhere on the network?
Do I need a dedicated pc or server?

we provide mobile internet access to our customer...
i will be able to analyze all that traffic

I have one cisco 7204 router connected to several switches.
let me know if you need more info.

Thanks,
Paul