ah for a lap, so you will have to replace the optical drive with a tray that supports a secondary HDD/SSD
try to get a SSD with at least 90GB capacity so you can put some frequently used programs along with the OS.
hybrids are almost as good as SSDs plus higher capacities. try reading some articles, im not much familiar with them. you might consider selling your HDD and put money together to buy a hybrid so you can use the available single slot, save the optical drive and get better performance.