Many times it happens overnight. This step was put first because you can write down the adapter address or Mac address on the back of a 3Com brand card before you install the card and save time running winipcfg utility. This will discharge. Just walking across the carpeted floor or sitting in a cloth chair can build up several hundred volts that could fry chips in your computer. There should be screws on the back side of the case which need to be removed.
Some cases come apart differently.
Please refer to your users manual for further clarification. You have either an ISA or PCI Ethernet card. Look at the graphic below. Your card would plug into one of these types of slots. One slot has many more pins than the other.