I am using Scrivener to write a book on my new 27 in iMac with Lion installed. I use Dropbox to write in Scrivener, on occasion, with my Macbook Pro as well. Is there a way to access Scrivener on a new ipad?
Not yet, such is the purpose of this forum. 
It’s still in the early development and design phases.
What you can do, which is what people have been using for mobile integration since 2.x was released, is take advantage of its synchronisation tools. You’ll find these outlined and described in detail in chapter 13 of the user manual PDF. There are tools for Index Card and Simplenote, and then a general tool which works with any text editor on the iPad that can browse and edit files on Dropbox.
There are a number of apps that allow you to access your computer monitor from your ipad. Splashtop is one of them. Remoter VNC (which I haven’t used much) is another one. There is plenty. You have your options, it’s just a matter of choosing the one you like. I must say I haven’t been impressed by these apps, I prefer to use text editors on the iPad and sync the changes, but you should give it a try. Perhaps you like that approach.
My experience has been the same. It’s very difficult to properly convert what a full keyboard and pointer can do, to a finger. So the interface differences are sometimes tough to get around. It’s also not very viable unless you are at home. Doing this over the Internet is very slow. Some do swear by it though! Pity most of them don’t have a demo.