Ok, let's see... I'm not exactly a mapper, but I once fooled around with Hammer a bit, and among the few things I eventually got to work were some ladders...
1. On the wall where you want the ladder to be, draw a block that has the shape of a ladder (i.e. as high as the wall, approx. as wide as a player and quite thin. [height of the wall] / 32 units in width / 4 units thick ought to do the trick. Right-click and select "create block".
2. Now you have a block, but it's covered with this ugly default texture. If you want to get ladder textures, make sure that you told Hammer which wad files to open by default. It should at least open hl.wad and cstrike.wad. The standard ladder textures are all in hl.wad. Go to that texture browsing window (forgot the exact name), and in the "filter" text box, enter "ladder". Now all textures that have the name "ladder" in them will show up. Select the texture you like and apply it to the block.
3. Fine - now you ought to have a block in the correct size and with the correct texture on it, but (a) the spaces between the rungs are blue and not transparent as they should, and (b) you can't climb up so far. So first align the texture to the block so that it looks nice & clean. Then right-click the block and select "tie to entity". In the following window, select "func_wall" in that dropdown list under "Class:". Under "attributes", click "Render Mode" and select "solid". Under "FX Amount", select / enter "1". Under "FX Color", enter "0 0 255". This will make the ugly blue disappear - now your ladder should really look like a ladder.
4. Ok, so it looks like a ladder, but it still doesn't work like one. Create a further block with the same dimensions as the ladder, i.e. as high as the ladder, as wide as the ladder and very thin. You don't have to worry about textures here since the block will be invisible in game. Once again, select "tie to entity", but this time make it a func_ladder (duh!) by selecting "func_ladder" under "Class:".
Theoretically, you should have a nice working ladder now.
NOTE: I would guess that the first block (the one that looks like a ladder) is not absolutely necessary. If you have a wall covered with a texture that looks like anything you can climb (e.g. ivy), you can just place the func_ladder in front of it, and in game you'll be able to climb up there.
Hope this bit helped some... good luck!
EDIT
OMG, "4 units thick ought to do the trick"... looks like I'm having my poetic 5 minutes right now... someone had better stop me
Oh, and since you are our newest member and just posted here for the first time (hopefully not the last), let me welcome you here in the name of all the nice folks who like to hang around at this place... you'll like it, I hope! Cheers!
