When it was new it ran plenty fast enough for you with the same amount of memory that you have now - unless you've started running a really complex database package with multiple enquiries and multiple users you very probably have enough RAM. Memory is quite cheap so you might think about adding more if it makes you feel better.
What happens over time is that naughty things get into the startup list - software that's pre-loaded at start time and malicious software or Malware (spyware) that reports your web browsing habits back to one or probably serveral marketing companies. All kinds of wicked software runs in the background without your knowledge.
In Vista, Windows Defender - Software Explorer - will allow you to delete all entries in the startup list. Under XP typing msconfig in the RUN box and clicking OK.
Select the startup option and deselect everything.
Download and run Spybot Search & Destroy (free)
It will probably find dozens or even hundreds of "bad" things in your machine - have Spybot fix the problems. Run Spybot weekly or monthly.
Download Piriform's Ccleaner and run the registry tidy-up tool (some experts say this is not necessary and they may be right)
Defragmnent your disk - and do it annually.
Consider running Mozilla's Firefox browser (free) instead of Microsoft's Internet Explorer.
Consider a free anti-virus package such as AVG
These are the things I do on my machines and I have no problems with them running slower and slower.
Make friends with the Task Manager - right click on the taskbar and check what applications are running, what processes, machine performance and networking are doing.
Good luck...
Peccavi, January 2010
