lol, think I'm gonna regret going here - outa my league
Lets say your map is called Myschool.map
1. Choose a current wall texture that you want to modify, lets say texture 40.
2. Create your 2D picture etc in PaintShop Pro or whatever you use, make it large, say 512 x 512.
3. Save it as Tile40.png or a .jpg
4. Create a DEF file as follows and save it as Myschool.def
texture 40 { pal 0 { file "Tile40.png" } }
5. Using winzip zip the 2 files (Tile40.png and Myschool.def) to a file called Myschool_hrp.zip
6. In SwpBuild select the wall you want to display this and put texture 40 on it.
NB. In Build it will look like the original but when you play the map your new texture will be visible.
To see the texture in build is possible but requires knowledge on modifying a .ART file.
7. Make sure this Myschool_hrp.zip file is in the same place as your Myschool.map