At a minimum, you will require:
Inexpensive three-button mice, trackballs, and touchpads manufactured by Logitech and many others are widely available for PCs, and are highly recommended if you do much annotation editing. Most are fully compatible with Microsoft two-button mice. Some users prefer trackballs for precision editing since there is no tendency for the pointer to move when clicking the buttons, as with a mouse. Future versions of WAVE will make use of scroll wheels on mice when available; if you choose a mouse equipped with a scroll wheel, try to select one that allows you to use the middle button without generating scroll wheel events.
For those on a tight budget, suitable used PCs are often available for next to nothing. If you use an older PC and can afford to upgrade components, get a new three-button mouse or trackball first, a new monitor if the old one is inadequate, more memory if you have less than 64 Mb, a new IDE disk drive (around US$100) if yours is more than 3 years old, and only then consider other performance upgrades such as a faster CPU. Although Linux does not require large amounts of RAM, it can use additional RAM very effectively, and you are likely to find that purchasing (say) 16 or 32 Mb of additional RAM results in a bigger performance improvement than spending the same amount on a faster CPU.
Although WAVE now runs on MS-Windows, we still recommend using GNU/Linux as the platform of choice because of its greater speed, capability, configurability, security, and stability, and because of the wider range of related software available for GNU/Linux. Other WAVE users have reported success on PCs running FreeBSD. Macintoshes running OS X and SPARC-based systems may also be worth considering, although they tend to be substantially more expensive than comparable or faster Linux or FreeBSD PCs.