1. Scan for viruses
2. remove any none essential programs from starting at start up
3. Run disk clean
4. Defrag hard drive
Easiest thing to do since it usually is multiply issues is to backup all your files and do a clean install so its just like new again not a repair. Whether you realize it or not programs get installed you may not know about or are starting up that dont need to be. Along with malware, spyware, bad/dead drivers the list goes on. Just like a car routine maintence is needed and if not properly maintained an overhaul every once in a while should be done.
My sisters old laptop was just the same way it only had 512mb of ram and a 1.8ghz dual core centrino on XP. Wiped the hard drive and put another 512mb in it with Win7 and it does just fine though she got another anyway oh well free laptop for me.
More Advanced Micro Devices than Intel