i started out with a ver basic pc that had a celeron E3500 dual core processor and 4g of ram. i first added a SSD that helped boot time incredibly but didnt do much for lightroom. then i added another 4G of ram that help a little but not much. i finally bit the bullet and bought a new motherboard and I5 4570 processor with 8G of ram. WOW what a difference ! i can scroll through previews in lightroom as fast as scrolling a page on facebook lol.
image exporting is also at least 5 times faster. now when exporting more than 5 images the computer doesnt freeze any more lol. i know its not top of the line but the improvement is outstanding.