Two hard drive performance considerations to consider with desktop configurations:

1) Consider getting a 10,000rpm hard drive.  These are lightening fast and can make a big difference over the default 7,200rpm drives that typically come with desktops (Jeff Atwood has a good blog post recommending one of these). 

2) Consider buying a second physical hard drive and setup your operating system and OS virtual memory swap file to use one of the physical drives, and then store all your data (images, documents and Visual Studio projects) on the second physical drive.  The benefit of an approach like this is that your read/write data operations won't be competing for disk I/O activity with the operating system updating the virtual memory file.