Pentium D 2.8ghz vs P4 HT 3.0ghz?

Would a Pentium D running at 2.8ghz be much of an upgrade from my current P4 3ghz HT system? Also, how good is Windows 7 at managing CPU cores when it comes to software designed for a single core system? For example, would windows see that I am trying to run something (like say, Oblivion) that has a heavy CPU load and automatically send it to an unused core or would it be necessary to do that manually?

Most Games use Dual core you can get TRIcore I think AMD offers this one though not intel or Quad core

But that is up to you more cores help with applications and processes

so you have to think what works for you

There is a huge gap in performance between those two processors. The Pentium D offers a newer, more efficient core and an increased cache....plus a second core as well. The OS will effectively manage the hardware resources available to it, so you would just run the game and enjoy.