Don't assume that your PC is compatible with a voice recognition product just because it meets the processor, RAM, and hard drive minimum system requirements listed on the product's box. Double-check the sound card requirements. Sound cards remain a crucial compatibility issue for many voice recognition products (specifically not all voice recognition products work with all sound cards.
Before you head to the store, jot down all the details you can about your sound card, including make, model, and integrated memory. You'll need to compare these against the minimum system requirements of your voice recognition product.