Hey basically I'm wondering if you can build your own VGA box with a couple of differen't inputs and possibly even a TV tuner?

Thanks
Erock

Anything can be build but its not going to be cheaper than the comercial units.
This is a pretty complicated box as a 17" LCD has 1280x1024 pixels 8bits of red, green and blue and has a frame rate of at least 60Hz so that means that you need to generate

1280x1024x3x60x1.3 pixels/sec = 306 Million bytes/sec

TV is NTSC which uses an interlaced format so all the even lines show up first then all the odd so you need to store one field to mix with the next to get a full screen image.

Then you need to deal with color space conversion and scaling and variable timings for different resolutions so this is a pretty difficult job for even an expereicenced engineer.