In short yes. As the processor has two cores it is able to deal with performing more than one function at a single time in a more efficient way than a traditionsal single core processor.
I have trialled an AMD Athlon X2 (the 4600+ model) and the speed increase is dependant upon what you are doing. For office applications it is noticably quicker, however for digital editting, video rendering (and games) it is blisteringly fast compared to a similar single cored processor. We tested on XP 64 so don't know how it would perform on XP Pro.
The one thing I will say is that if you alt-tab between applications the change is instant. Whether it's worth £500+ (for the 4600+) I don't know.