Firstly, there's a huge difference when you say Dual Core and Pentium D. There's a series of cpu called Core2Duo, which is newer and much, much, faster than the older Pentium Ds. A 1.8GHz C2D can take on a 3GHz Pentium D in some cases, while taking less power.
Pentium D belongs to the Pentium family while the Pentium Dual-core belongs to the C2D family. There are newer C2Ds out now, so the E4600 is rather outdated.
And yes, the 4400+ is better than the Pentium D 925.
Yes, Pentium D is a dual-core, meaning there's 2 cores.
The name Pentium Dual-Core is also a dual core cpu, but from the C2D family. Intel just decided to make it confusing to us consumers. There is a huge difference between Pentium D and Pentium Dual-Core (Dual-Core as in the name).
About the Athlon X2 4400 vs. Dual Core E2200, the link for benchmarks on rendering shows an indirect comparison, but the information is there.
The timing for the 2.3 GHz X2 4400 are up (114), but the closest results for the 2.2 GHz E2200 Dual Core are the 1.8 GHz E2160 Dual Core (114), which indicates the E2200 would be faster than the E2160, which is the same as the X2 4400.
Still, the desktops on sale at the moment are over $100 cheaper for the Athlon X2 4400's, compared to the Dual Core E2200's and so on this Black Friday, I'll be getting the Athlon.,