The requirements don't seem too bad, even for those with a budget rig will be able to handle this one at reasonable settings without too many problems.
Minimum System Requirements :
Windows Vista/XP
AMD 64 3200+ or Intel Pentium 4 3.0GHz
512 MB RAM (XP) / 1 GB RAM (Vista)
Shader 3.0 or better 256 MB:
nVidia GeForce 6600GT
ATI Radeon 1600XT
16 GB free hard drive space
The amount of hard drive space seems a bit excessive given the expected short length of the single player campaign and running on the same engine as Call of Duty 4: Modern Warfare. Maybe it's all those IWNET install files taking up your hard drive?
Call of Duty: Modern Warfare 2 is out from 10 November on Xbox 360, PlayStation 3 and PC sans dedicated server files.
http://clanbase.ggl.com/news.php?nid=329824