I have not tried using Dennnis's Knife plugin ... but I'm sure it will work fine.
There are several ways I use to do the kind of thing you want. Technique below is one I use to put labels on bottles (for example).
I'm making the assumption the curved surface is like a column but technique will work on all types of curved surfaces too.
1. Create an ellipse (16 points works well for a column).
2. Extrude the ellipse 4 times (deleting orginal surface as you go).
3. In vertex mode, hilite the vertices that describe four surfaces in centre of the object (see the pic below wireframe on left)
4. Now Surface--->Cut away Object. (End result is solid object on right coloured to show the two objects you now have).
5. Apply your poster texture to the new object (red one). If curvature of wall is large you may have to tweak the texture in the texture editor, or if really large use UVMapper to map it to a cylinder.
Tweak the spacing between each extrusion to get your poster fitting properly .
You can repeat the cutouts around the pillar at essentially 90 degree intervals ... so you could have 4 posters on a pillar.
Hope that helps,
griff
