a) Sudan has the responsibility during all circumstances for the protection of civilians.
b) UNAMIS is of course also bound by international law to abide by humanitarian law
c) There is a legal basis for intervention
d) The invitation of Sudan is solely a diplomatic opening
However: There seem to be some legal discussions wheter the resolution is a clear chapter VII or more like chapter VI and a half. There is a trend, as seen in Lebanon and other, that one use the wordings and language of a chapter VII mission but in a VI resolution. Apparently the deal is, that this gives the force the possibility of pulling out if the missions turns out to be a disaster. That is a lot more difficult with a chapter VII mission, since you are almost legally bound to finish the job.
I am sorry that I am not able to give a clear answer. I am investigating more, and will hopefully return with a clear answer. If there is one.
For me though, it seems like a clear chapter VII. Andreas The Oslo Blog - www.akiaby.dk