You should be able to copy most any mod or map, but you have to place them in the appropriate directory. Follow the directions that the mod or map gives you. If it is a map you are installing then place it in \quake\ID1\maps.
If you're installing a mod then it should have it's own directory (\quake\modname) and be activated through a command line. You can get this Run option by holding your stylus down on the clock in the upper right hand corner for 3 seconds. Then tap Run, then type in "\quake\pocketquake.exe -modname"
Some mods are not designed for speed in mind and will not play very well on the PocketPC version of Quake. The same goes for maps. Just about everything that works well with Quake is located on the PocketQuake website () in the downloads section. There is an extensive section for maps and bots that have been modified to work quite well with PocketQuake. I suggest you try those first.