i have 2 ISP, each ISP is 20Mbps internet speed.. and i connect this 2 ISP to mikrotik router, so this network will have 20Mbps + 20Mbps line...
and this network have 150 users..

any idea how to set the QoS?

i don't want the user using p2p application will use the Full bandwidth then affect the others user become slow browsing...
how can i do that?

and i want reserve some bandwidth for some user for gaming..

any idea?

Have a look at this:
http://wiki.mikrotik.com/wiki/Connection_Rate