Don't know if this helps, but I have a USB wireless adapter plugged into my Tivo series II, which allows it to connect to my wireless router and download the programming guide. I can also stream media to my Tivo this way.
The 990 would have to have a driver or something built-in to do this, as I had to plug my Tivo into a regular phone line after I bought it, in order to get it to dail up to Tivo Central and download the latest firmware to allow the wireless networking to function.