The Now TV app isn't available on any Virgin Media set top box.
However, you are absolutely right about the TiVo boxes being slow. The only effective solution to this is to upgrade to the V6 box which is much faster and in most cases now only costs £20. However, if you re-contract your services for another 12 months, they may give you one for free as part of that deal.
Best people to speak to should you take this avenue is retentions, the "thinking of leaving us" option when you call up. See what they say. Mention the issues you've been having but in a polite way, the trick is to make them want to give you a good deal so a bit of charm will go a long way.
Thanks for your reply - The NOW TV is through my LG Smart TV and keeps freezing along with YOUTUBE which i view through the Tivo box and also the smart tv. I queried my internet with them but they run some tests saying all well. Im at a loss because I'm using Youtube and Now tv more and more. I may try to get a V6 box to see if this improves the Youtube and slowness of my TIVO