The most common practice is to recreate the web page in Photoshop (at the highest resolution you might need), Illustrator, or After Effects and then animate in After Effects.
You could do a screen capture of the website, but that's often not in a high-enough resolution.
You have not told us the final use of this project. If it's a video, then AE is a good choice as the tool to do this animation. If you are trying to build a web page and you need mobile compatibility then Flash is not the answer, you'll need HTML 5.
The only problem that I see if you are creating a video is the first line of your post - high rez still image of a website page. Every time I have had to do this it has required either recreating the website from scratch in Illustrator or Photoshop, modifying line widths, font sizes and in some cases colors or bringing a screen cap of the website into Photoshop and fixing all the thin lines. What I'm saying is that an image like this will not work at all in a video if you move it, scale it, or make it a 3D layer and put it at an angle to the camera.
Thats very helpful thanks. I'll take a look at the discussion cheers!