1- i dont know if i have to configure manually the "clients.conf" file and it will be automatically written on mysql database or conversely, i would write my data on mysql manually and those data will be automatically writted on text files?
No.
maybe , i think there are independent of each.
Yes. Just don't add same client to both.
2- I have a 3Com Total control making dial-up authorizations; now, i need to use radius to pppoe ,for aaa. i think i will use the HiperARC card, so i think my model in clients.conf isn't "tc", it is usrhiper, right?
Pass. Someone with equipment like yours will be able to help you.
3- I'm very, very confused in this : who does bandwidth limitation for a user? i.e.: "Joe" must have 128Kbps of traffic limitation.
pppoe server does (3Com)?
Yes.
or radius does somehow?
No.
or maybe freeradius send parameters to 3com hiper arc to set it ?
Yes, that can be done in many cases. Depends if NAS supports bandwidth limiting VSAs. Ivan Kalik