If u are familiar with the computer parts. Yes, doing it is fun and no problems. Sim Lim Square (SLS) is the best place to shop for parts. I can spend the whole day there just collecting the pricelist and do comparison and end up buying wat I want the following week
If u are not, please do read up first, there are many good books in our local national/regional libaries or the internet that provide such information. I have come across many incidents, ppl brought the wrong parts, went back to the store to make a big hoo-ha out of it which in the first place they are in the wrong (failing to read up).
(example: buying a top of the range PCIe video card for their 3D gaming home to find out that their board only support AGP which they should have found first before purchase.)