FS Global 2008 is NOT "just FS Global 2005 with a new name and a new package".
FS Global 2008 is a new product. It uses the NEWEST SRTM data (released by NASA in late 2006!) plus additional data from various sources. Resolution in some parts has been improved to 19m (!). Yes, this is 4 times better than FS Global 2005 and up to 63 times better than FS itself! And yes, even than FSX! Default SRTM coverage in FSX is VERY small compared to the whole world!
FS Global 2008 comes in two versions in one box, which makes it 6 DVDs. One version is for FS 2004 and one for FSX. Microsoft has considerably improved scenery management and interaction of scenery types within FSX. The new scenery concepts provide a more detailed and realistic far-distance view, textures adapt better to the mesh, the FSX default scenery is more precise and causes less (optical) conflicts and last but not least FSX offers more functionality for a seamless integration of mesh and vector scenery.
FS Global 2008 (FSX version) takes use of all these enhancements of FSX.
You don't have FSX yet? Well, upgrade your existing FS Global 2005 world to FS Global 2008 then and enjoy the enhanced resolution, new data and various improvements in concept until you are reday for FSX.