Lightroom Question

[vandrv]

I'm not sure if this is exactly the right forum for this question, but here goes. I have both a core 2 duo Imac and a core two duo Macbook Pro that seem to be struggling with Lightroom 4. I have only one catalog with probably about thirty thousand photos in it and if I select all photos, it takes forever to generate previews. I would really rather not separate the photos into smaller categories to keep it easier to search for a particular photo. My question concerns whether I should purchase a new computer or would installing an SSD in one pick the speed up enough to be usable? All my photos are stored on an external hard drive if that makes a difference. I'm not quite sure where or how previews are generated. Thanks for any help