Windows users are sometimes tempted to try OS X, but I don’t recommend it.
Getting a Hackintosh to work is a real pain, OS X isn’t more forgiving to old hardware, and it’s not free..
Internal temperatures rise, reducing the efficiency of your hardware.
As the problem worsens some components may have to throttle their performance, slowing your laptop down. All laptops, even Apple’s unibody Mac Books, can have their internals accessed by removing the bottom panel.
This usually requires that you take out a number of screws and then use a small, sharp object to pry the panel off.
Remove that panel and you can upgrade without disassembling the entire laptop.
There may even be instructions in your laptop’s manual.
If you’re running an older version of Windows, particularly Vista, going to Windows 7 is worthwhile (though also expensive, and again, you may feel spending so much on an old laptop is unwise).