For snapping to an iso grid first convert the mouse coordinates into isometric:
isoX = MouseY + MouseX / 2
isoY = MouseY - MouseX / 2
But to snap to a grid you need to do math like this: round(n/32)*32
isoX = round((MouseY + MouseX / 2) / 32 - 32) * 32
isoY = round((MouseY - MouseX / 2) / 32) * 32
Note: the -32 in bold to correct the hotspot being on the top left.
Then convert back to regular coordinates:
X = isoX - isoY
Y = (isoX + isoY) /2
aznmonkeyboy
Changed my example a bit so that scrolling isn't faked. The tiles are just moved to the other side when they leave the screen. This should be as easy to work with as if all the tiles existed at once.
http://dl.dropbox.com/u/5426011/examples11/tileScroll2.cap
I'm still using sprites, it's just a preference. Sprites provide the luxury of hotspots so you can easily have different height tiles. TledBackgrounds have the advantage of rendering almost twice as fast as sprites, but I'm getting a constant 60 fps so it's fast enough.