I'm not sure if there is any difference in resolution. I've asked guy selling them on Ebay and he said the only difference is gigabit ethernet...
7970g is Cisco inline power and 802.3af compliant
7971g is only 802.3af compliant NOT Cisco inline power compliant
7970g is 10/100 Mbps
7971g is 10/100/1000 Mbps
7970g won't get full brightness if powered over ethernet
7971g will get full brightness if powered over ethernet (I think !!???)