put it this way. do you have an NIC laying around, or have you been using onboard LAN for so long now that you've gotten rid of any NIC's you may have had? if that's the case, you are going to have to spend another $15-$20 for a cheap NIC. if you are set on using the 875P chipset, i'd get at least the IC7-G. otherwise the IS7 is fine, and gives you onboard LAN. the only other major difference between the two boards i think is that the IC7 has intel PAT technology, whereas the IS7 only has Abit's GAT, which is an emulated version of PAT, and it only works w/ certain memory dividers and fsb's, i so i don't even mess with it.
EDIT: i hear some people say that the 875P chipset is more likely to hit higher fsb speeds, i think due to the binning of the chips intel uses to make the 875 and 865 chipsets, but don't quote me on that...