The first thing you have to figure out is if the phone is even running SIP firmware. Those phones when originally manufactured were shipped with SCCP firmware.
The easiest way to do this is setup your TFTP server to hand out the Cisco-phone specific info and then look in your TFTP server logs to see if the phone is attempting to load a firmware file that starts with P00 or P0S
If P0S then it’s running SIP if P00 then it’s got SCCP firmware on it. You will have to update it to SIP.
This isn’t trivial. If you are really really REALLY interested in doing this I can post a lot of info on how to do it but I don’t want to spend the time posting it if all your going to do is read it, and think “that’s too much work” and then not do it.
The reality is that there are many other Cisco models that are newer such as the 88xx series that are very cheap and have a lot more cooler features (such as video) Getting your 7970 running can be done but it’s in the camp of “I can call myself a FreePBX God if I can do this” instead of “I just want to play with a cheap phone” So what do you want?