Well thats a vague request! How about a VCR? or a dvd player. the composite video out is a video signal Failing that, google 'composite video generation using microcontroller'. PIC's were often used to produce basic NTSC/PAL signals, the newer (and faster) AVR's soon took over. Even CPLD's/FPGA's are used for higher resolution and more colours.
Well, considering the virtex 4 is an FPGA (a huge one at that) your 'infomation' could be anything, in any format. I'm not trying to sound patronizing, or stupid, but In order to produce a VGA signal, you really need to know exactly what you are trying to display. Is this pure plain old video from an MPEG decoder? Are you trying ti display characters/numbers/menu system?
Also note VGA is a bit different from 'video' standards, with separate RGB components - which is actually easier to generate over fully encoded composite video ala NTSC/PSL/SECAM. Xilinx has PLENTY of application notes on outputting VGA from its devices, and 'XESS' boards often have a VGA connector with resistor DAC's for this very purpose.
I'm sure they provide some evaulation VHDL/verilog which you can use. Failing that, Home :: OpenCores has plenty of open source IP cores.
Without know what is producing this 'information', I can be much help. But you won't need a seperate chip to generate VGA, its surprisingly straight forward in large FPGA's.