I'm currently using a 2.6.35-rc3 Zen kernel and I'm trying to get my Radeon HD 2400's temperature. I've looked into my dmesg but I don't know what I'm looking for... Any pointers please? 
The only i2c I can see here is that i801, which I assume is from my motherboard, and it is already built into my kernel. sensors-detect does see something related to my Radeon, but no thermal monitoring there:
Code:
Next adapter: Radeon i2c bit bus DVI (i2c-1)
Do you want to scan it? (YES/no/selectively):
Client found at address 0x50
Probing for `Analog Devices ADM1033'... No
Probing for `Analog Devices ADM1034'... No
Probing for `SPD EEPROM'... No
Probing for `EDID EEPROM'... Yes
(confidence 8, not a hardware monitoring chip)
Thanks for any input.