hi,
i have a project on making a video capture card using FPGA. VGA
at the input and output is taken at USB 2.0 port . that video should
be displayed and could be stored on some media player.
Please help
thanxs

Capturing VGA signals isn't so easy because you need fast AD conversion. You can check the Analog Devices webpage because they sell some IC's that gives you an 8b or 10b output with horizontal and vertical syncs.

Can't you use DVI or HDMI? This signals can be "read" directly from the pins of the FPGA (Spartan 3A family supports TMDS).

best regards,
Diego.

can a VGA core help me in this regard. can i use VGA core on FPGA
for the input VGA signals or is it used only for the output signals?
Would A/D conversion still be necessary?

I think that the VGA core is only output. Outputting VGA signals is really easy because the D/A converter is made with only an array of resistors.
To read the VGA signals only require the A/D converter if you want to read the color. If you want to read this in monochrome, you can bypass this converters but i think that this is not what you are looking for.
The signals R, G and B (colors) are from 0v to 0.7v so with an 8 bits ADC you can get 8 bits per color and with 10 bits you can 10 bits per color and so on...
The vertical and horizontal syncs (HS and VS) are digital only and this can be read with the FPGA with no extra hardware.
Instead of looking to put three ADC, you may look in analog.com to a single IC VGA decoder.

May this device be useful to you? this is really cheap and you must do nothing :P
http://www.tigerdirect.com/applications/SearchTools/item-details.asp?EdpNo=3504456&CatId=1428

Thanks for replying,
If i ADC the VGA input signal, then would i be using the VGA port
or DVI port on FPGA kit for the convrted signal. If i can use the DVI port then
will i be able to use the DVI core or it is also an output DVI core.
Thanks,

If you are able to use DVI as video input, you may read the document xapp460 (google it) where shows how to use the DVI as input/output with an Spartan 3A.
The DVI is a digital protocol and you must read the specification (it's free), it is a bit more complicated than VGA but no need external hardware.
Caution: you cannot use an DVI to VGA cable because this only maps from the DVI the analog signals that are also present in the connector to the VGA! for you the only signals useful are the four TMDS pairs (when you watch for the dvi pinout you will see this pairs and the analog signals for DVI-I connector).
For the core, i don't know because i haven't used no one.

Regards,
Diego.

For DVI, you can use a DVI chip from AD or SiliconImage, it will handle the DVI protocol for you and you just need to interface the Pixel Data.

http://www.siliconimage.com/products/family.aspx?id=8

If you are looking for VGA resolution (640x480x60) then the app note from Xilinx should be enough for you, but if you are looking for higher resolutions then you need to have a DVI receiver chip to be able to handle the high bandwidth of the DVI signals.

You can take a look at this board from Analog device which will give you some ideas about how you can handle this problem:

http://www.analog.com/static/imported-files/application_notes/54068955945250AN_784_0.pdf

Also, you can use this cheap board that supports resolutions from VGA to UXGA:

http://www.bitec.ltd.uk/sc_dviin.html

Best regards,
/Farhad Abdolian