Refer to Tony Hopinson's post about chasing upgrades. You could end up spending a lot of money just because you wanted newer faster desktop hardware. As Tony noted, new hardware leads to new OS leads to new version of applications. Many thousands of dollars later you still have to deal with the original problem, that stupid application. It's time for your management to make the tough decision of abandoning this white elephant application and finding a more reliable replacement. Spending more money just to get this trouble application to work properly is a mistake. Chances are good that some other, more reliable, software vendor already has a mature product that will do what you need to have done.
The fact that this application is running on desktop computers seems very questionable. If you need to run a lot of statistical analyses on large databases you might find that a central server is a better solution. Also, you might find that network congestion is really your problem. If you have this application sharing files between desktop computers you have got a very bad configuration. It is possible that even if you just move the data files to a central file server you would see an improvement in performance.
As I said before, your problem may not be slow hardware. It could be your configuration, which might only marginally benefit from newer hardware. It could be that you need a central database server OR a central file server. And most especially you may benefit most if you find another software application to do the work that you need to have done.
