W1900 19" LCD TV DISPAY - Use as computer monitor - use of both DVI and VGA inputs

Does anybody know if this display can be used to connect two computers - one to the VGA and one to the DVI input.  I currently use this configuration with an older Dell monitor with no problems.  (The documentation says only to use one of the connections but I'm guessing this is when connecting a single computer).

Also has anybody any experience of setting up a three/four monitor display for a single PC?  I gather that it requires another graphics card but I'm wondering if the VGA output from the integrated graphics can be used where a grahics card is installed. i.e. there are already three monitor outputs on the PC.

Thanks