There are two scenarios really but one of them depends on the chip-set of the motherboard. If you go with a Z68 board, it supports Intel Smart Response Technology (SRT). This technology allows you to use an SSD (up to 64GB) for hard drive caching. This is setup along with the OS. SRT will speed up the overall performance and make your spin drive faster as well.
The most expensive but best performance scenario is to use a larger SSD (120GB or larger) and install the OS and applications on it and have your spin drive as a data drive. This scenario is not dependent on any chip-set. If money is not an issue, get the largest SSD you can afford.
AnandTech - Intel Z68 Chipset & Smart Response Technology (SSD Caching) Review