i wanted to hook up various things to my 7800gt, via vivo, but is there some sort of software i need to view it.
For video in, you'll need to install the NVIDIA WDM capture drivers. They should be available on the driver CD that came with your card or NVIDIA's website.
If you just want to watch something (eg ps2) then I'd recomend ATV2000, I managed to play on the PS2 using it without any noticible lag, and it's free For recording stuff, er, dunno, but window's moviemaker will work with the WDM drivers should you be feeling too cheap to look for anything better... (edit, btw, make sure you do get the up to date drivers from nVidia, I had big problems with them on my 6600GT before...)
i would also like to use the vivo on my card, which cable should i use of the mass assortment that came with my card?
Dunno, rtfm? On most cards it's the cable that plugs into the connector that's not the DVI or VGA (D-Sub) plug...