Stuffes up when click on texture pic and no textuersand stuff up in 3d mode

[Twistedpsp]

When i used a demo.wad i doo it coredtly following a guide and then when i get into the editor i click on the box shaped tool click on a wall then right click on it and walla the texture box opens and it haas where the textuter pic is soposed to be it says not found and when i click on it goes runtime erroe 9 and closes and i dont have anny textures in the first place wher do i download a texture pack? Andd when i'm in 3D MODE and i click it goes runtime error 9 and closes.

HELP ME I RELLY WANNA MAKE A WAD TO PLAY ON MY PSP PLEASE HELP ME