Dude, you were right there.
Navigate: Home page -> Products -> Software -> Voice Systems
There's a handy popup menu to select different versions of ViaVoice, and right below it a link to "IBM ViaVoice for Windows, Release 8!".
Lotus software is listed under "Software" because it's, well, software.
The reason it's sometimes difficult, but by no means impossible, to navigate IBM's Web site is because there's so much information there. Microsoft's is the same way. When I was first working as a web programmer for NCSA, though, that was the definition of a navigational nightmare.
Besides, when all else fails, you're expected to use the search engine. That's why it's right there, near the top of the page.