The Processor in these machines runs at 1.6gHz or more which is plenty fast enough - what you probably need to do is to sort out all the dross that's running in the background without your knowledge and stealing disk and processor resources.
Right Click on the empty space of the Task Bar along the bottom of the screen - select Task Manager / Processes - In the CPU column you will see what's eating the machine - mine has my Firefox Browser at about 3% and System Idle varying from 91 to 97%
Get the following free software from the internet...
Piriform's CCleaner
Microsoft's Windows Defender (you may have this already)
Spybot Search & Destroy.
Use the Tools / Software Explorer feature of Windows Defender and examine the Start up list - take out anything that's not needed - leave in the Microsoft stuff, Intel (processor) stuff and anything security related.
Run Spybot and use it to remove any malware - there will probably be quite a bit the first time you run it.
Use the Registry feature of C Cleaner to tidy up your computer's registry.
Defragment your disk(s)
All this may take an hour or so.
Reboot the machine and use W Defender to see what programmes are currently running - make a note of anything suspicious and use the Add/Delete programs utility in control panel to get rid of anything suspicious.
Run Spybot weekly.
The machine should now be running only the programmes that You want it to be running.
Others will say ADD MEMORY which is fine but it won't necessarily help and has a cost associated with it. Your internet connection and its speed will also have an impact depending on what you're doing.
Good luck...
Peccavi
March 2009