Can anyone tells me that is it possible to use Built in and external VGA's both at the same TIME and have output on 2 monitors.It is possible.
Plug both monitors in, reboot your PC, when windows comes up right click on the desktop and click Properties.
Click the Settings tab, you should see two monitors a 1 and a 2. Make sure that "Extend my Windows desktop onto this monitor" is checked on both monitors. Click Apply, click ok.
You should now have both monitors working.
If you want to change the way the monitors are related (Which one is on the left or right, etc...) then just go back to the Properites, Settings tab and click on the monitor you want to move and drag it to where you want it to be.Is this a laptop or desktop computer? If a laptop, you should be able to connect an external monitor and use both it and your laptop screen.

If a desktop, I think it DEPENDS on your motherboard. Some will allow you to do this; OTHERS will not.

By "Built in", I presume you mean onboard/integrated VIDEO. For the "external" monitor, would you be using a PCI Express video card, or would it be AGP or PCI? Do you ALREADY have the video card? If so, what connectors (VGA/D-sub, DVI, S-Video) does it have?