Neither of those features is a basic part of CHDK, Simone. It's possible to trigger the shutter via the USB port, but NOT from a PC - the triggering requires a power pulse (i.e. on then off) but if you connect the camera to a PC the power is there until you disconnect. People use a simple switch + battery combination to do the job.
As for accessing shots directly from a PC, there are some special CHDK builds that let you do that (search on PTP) but it's experimental and only available for a few cameras.
You don't say what camera you have - some older Canon cameras can be controlled in the way you want using software (but not CHDK or SDM).