Neither of those boards have onboard graphics. Both are Nforce2-ultra 400 and they have slightly different features, the 7NNXP has a DPS slot, more ethernet options and an AGP pro vs an AGP 8x slot.
For what your using it for, take your choice, both should be roughly equivalent.
www.tomshardware.com will have more information.
You may find a related board with onboard graphics, in which case it will be a Geforce 4 MX, which is the best onboard graphics solution available. Might save some money.