This can get somewhat complicated, but there are some things about HT to keep in mind. First and foremost, the acronym HT means different things for different vendors.
For Intel, it means "Hypthreading" (also called SMT or "Simultaneous Multi-Threading), which is a way of being able to execute two non-dependent instructions simultaneously in order to get a performance increase. In any application that runs faster with "Hyperthreading" than without, it will probably run even faster on a dual core or dual CPU system. AMD doesn't never produced "Hyperthreading" CPUs, based on the belief that the performance benefit would be negligible and that they would be producing true dual core CPUs soon enough.
AMD does not have any CPUs that support "Hyperthreading". To AMD, HT means "Hypertransport", which is a high-speed direct-connect interface that is used to connect CPUs to other system components (like CPU <-> chipset southbridge chip). Hyperthreading and Hypertransport are not related in any way.
Now as regards hyperthreading + dual core, only a very limited number of CPUs were produced by Intel that supported both, and I believe that they were all Extreme Edition pentium CPUs (though not all EE's were dual core and HT).
If you heart is set on dual core, but your budget is entry level, the Athlon 64 X2 3800+ (which I believe was the $150 CPU) will run circles around the Pentium D 805, and most of the rest of the Pentium D line. If you spend a little more money you can get a Core 2 Duo for $185, which should be a fair bit faster than the X2 3800+. But check Tom's site as paparazi suggested if you want the low-down on all of the possible permutations.
