Welcome to the forum.
Before buying a new sound card, can you try the device on another computer, preferably one running WinXP or Win7? Vista wasn’t exactly known for it’s speed or compatibilty, so make sure to eliminate it as the culprit before spending money.
Also, check the device settings both for the USB port it’s plugged into, and the device itself. They may not be configured correctly. Laptops are infamous for having slow or incorrectly configured USB ports, for example.