I'm using GtkRadiant for creating the bsp. You can get it from ID Softwares website. For the textures I'm using Jpegs. You should be able to find some tutorials for it around the web.
Once you've created your map you will need to compile it to a bsp using Radiant. For the texture zip them into a single zip file and give it the same name as your bsp file. Once you have done this rename the file extension to pk3.
You should end up with two files for example
myMap.bsp
myMap.zip
where myMap is your map name.
Once you have your two files add them as media to your dark basic pro project.
Then just add the following lines to set it up.
load bsp "myMap.pk3","myMap.bsp"
set bsp camera 0
set bsp camera collision 1,0,0.75,0
set bsp collision threshhold 1,0.001
automatic camera collision 0,0.5,4
You will need to add a loop with you control code and may need to play with the camera figures so they are correct for your map.
Hope this helps.
One last thing I think you may be able to include your bsp file in the pk3 file since patch 2 but I haven't tried it yet.