Since chipsets and video cards usually don't have any type of mounting system for a heatsink, it is usually easier to use a thermal epoxy such as Arctic Silver Thermal Adhesive instead of a thermal grease. Thermal epoxy works the same way other thermal compounds work except it has adhesive properties. When using thermal epoxy make sure to cover the entire contact surface of the chip evenly. Use enough epoxy to provide even coverage and proper grip, but not so much that the excess will squeeze out onto the circuit board. Allow several hours for the adhesive to dry before using the setup and be extra careful not to get any epoxy where you don't want it.
Most thermal epoxies come in a two part setup that includes a resin and curing agent.
To get proper coverage it is important to apply the adhesive while it is still in a liquid state. Look here for specific directions on applying Arctic Silver Thermal Adhesive . Thermal pads are not as messy as thermal compounds, but the performance of thermal pads is less than pastes. Thermal tape is very handy for mounting small heatsinks to video cards or chipsets instead of using epoxy. All thermal pastes have good performance when applied properly.