Internal Graphics and Discrete graphics ---- PROBLEM !!

when I installed my discrete graphics driver no problem but later afterwards when i installed the intel graphics driver the pc just when i log in becomes a bit slow! usally takes 7 seconds to start but now after installing the intel graphics driver it takes minimum 20 seconds for the display to come --- why?

my rig-----

i5 2400
nvidia geforce GTX 560
4GB RAM 1333bus A-TEAM (with heat sink)
Gigabyte GA Z68 MAD2HB3
720watts PSU
1TB HDD

now later i got pissed and uninstalled my intel graphics driver and everything was normal!
so how can i use now the discrete graphics only while playing game and rest of the time use internal graphics?
I have seen the internal graphics (same processore) on my frineds pc and he has no discrete graphics card but the movies are watchable in HD!
so now i wanna use the internal graphics.
What od i do and certainly also to avoid that problem of pc slowing down just when starting the pc??
Plesae help me people!!