Emulation is when you use Software as "virtual" Hardware.
This usually places a heavier burden on the CPU as opposed to using physical hardware. Causing a performance hit.
If it is true that GRAW does have some kind of emulating going on it'd be interesting to know how much. HOWEVER this may not be such a big hit on performance, if at all since now we have 3 cores (2 threads per core) each @3.2Ghz. (yummy)
Dont believe that person who wrote "it is a emulation". It is some idiot who is trying to get ppl worried. GRAW is using the ATI card which is using the new graphical effects, which the current xbox Nvidia chipset can not do.