Hi,
I saw your post while searching for the answer to a different problem. I'll just reply quickly as I'm flat out.
You should run 12.2.50 or later on your switch as there is all kinds of 802.1x features added and bugs fixed in that release. I run 12.2.52 and it works.
It sounds like your phone firmware does not support cdp 2nd port notification. That's the feature you need so that the phone uses CDP to tell the switch when the PC is plugged in which starts the dot1x authentication process.
This feature is only in reasonably recent phone firmware. I have a 7941 running 9.0.2SR1S and it is in there. I think the latest 8.x releases have it as well.
You also need to make sure your supplicant is setup correctly on your pc for dot1x to work, that depends on your OS.
Set those two things up for a start, that might help you.
CDP should show this: note the bit about 2nd port up
sh cdp nei det
-------------------------
Platform: Cisco IP Phone 7941, Capabilities: Host Phone Two-port Mac Relay
Interface: FastEthernet0/7, Port ID (outgoing port): Port 1
Holdtime : 158 sec
Second Port Status: Up
Version :
SCCP41.9-0-2SR1S
Hope this gets you moving.
Mike