From what I can recall of my old Pentium D, it wasn't really capable of running Red Orchestra Ost Front at a good framerate.
RO2 is going to be a CPU intensive game, plus UE3 is a bear as far as video performance is concerned. It's just a matter of getting modern hardware, though.
A Pentium D is really outdated. Get yourself a cheap Core 2 Duo or an AMD 3 core Phenom. Anything later than an nvidia 8800 GTS should be able to cover the video end of RO: HOS satisfactorily at moderate resolutions.
I myself have run plenty of UE3 games satisfactorily on my Core 2 Duo and nvidia 9600 GT, which is slightly slower than an 8800 GTS. For instance, Mass Effect, Bioshock, and Rainbow Six Vegas. Depending on how intensive HoS is, running it at medium low settings might be feasible for me.
But then again, you can't really know for sure until the requirements are released.
Take heart in the fact you shouldn't need to spend more than a few hundred dollars at most to totally destroy this game should you need an upgrade given where the hardware's at right now.