Hyperthreading is an Intel technlogy which basically simulates dual core processing on single dual chips. It does increase performance, but it will not provide the same results as literal dual core setup.
For your requirements, I would recommend a Celeron or Sempron. Yes, many people will tell you they are the lower end of the technology availible today, however unless you are doing larger, number crunching processes, you do not require an Athlon or Pentium.
The Celeron/Sempron route is the better choice for you in my opinion, you don't really need the larger cache size, and the L2 cache on some of these processors are starting to increase so they are not as bad as they are made out to be. Even better, they are much more cost effective processors.