If you only want to simply format the computer, just save all your important files or photos on it first, then find out all the softwares about the parts of your computer like mainboard driver or displaly card driver...etc, and running the computer by the 開機碟 enter the Dos system, type " Format C:" , after that then "D:E: F: "and so on the following step. Finally reinstall the operation system and all the softwares you need. That is all.
As for me myself, when getting virus I always FDISK my computer as well, in order to get rid of the virus totally la~~
I don't think format your PC is the best way. Since it require much computer installation experience such as boot, setup and config. If it is the first time you format the PC, I will not suggest you do so.
You can get rid of virus by the most updated viral scanner plus most updated virus definition file.
If you insist to format your PC, you should first make a harddisk image, e.g. using a software GHOST, to save it into different partition of your harddisk. If you have only one partition then you should write the image file into a CDR(s). In case you have some accident while formating or setting up your computer. you can get back this image file and restore to its previous condition.