LaptopMag has an interesting article entitled 5 Ways to Supercharge Your Laptop For Under US$100. It is an very interesting read, I suggest you visit it. Laptopmag's first recommendation, upgrading your by replacing the current hard drive with a Solid State Drive (SSD), is the best thing you can go with any laptop, whether old or brandnew.
The problem with SSD's is they are expensive. I would not recommend a drive smaller than 120 GB or 128 GB for a laptop, unless you have on of those than can hold two hard drives. After installing your operating system and some basic apps, a 60 GB or 64 GB SSD will give you 40 GB or less of space. Also from a price standpoint, it is not worth it. A 120 GB SSD drive costs about 50% more than a 60 GB SSD. A 90 GB SSD costs almost as much as a 120 GB unit.
Going to price, a 120 GB SSD will set you back a fairly hefty amount, between Php5,000 to Php7,000, depending on the brand and performance level. You will also be likely downgrading from 320 GB to 750 GB storage to 120 GB. But do you really need to drag all your store movies, videos, music and pictures everywhere you go?
You can covert your current hard drive to an external drive and place the new SSD in your laptop. One you have a laptop on an SSD, there is no going back. If you do not believe me. Just check out the benchmarks in 5 Ways to Supercharge Your Laptop For Under US$100.