type of cable to use???

O.K., Here goes…I set up a network using a DSL modem that runds into my router/print server….which runs to my switch which I have wired to my PC’s. All work now fine, BUT the building has prewired CAT5/RJ45 outlets in the offices, and I want to use that. But with the old users left they just cut the incoming cables to the computer room. SO MY QUESTION IS THIS what type of end do I use to go into the switch ( straight or crossover)?? AND what type of cable do I use to go from the wall outletto the PC??? thanks !!