It is not such a hard job. The hardest thing might be to confirm you are buying the right one. So why not take yours out of your PC and have it with you in the shop? Compare the one you want with your existing one. Easy!
When you have bought the one you want, look on the manufacturers website. They will probably have instructions on how to fit it. You should just be able to plug it in.
Next you have to reinstall your operating system and then all your software. This takes time, but is not complicated. Software is no good if it can't be installed by ordinary people. Just follow the instructions on screen.
Barry
June 2004