i dotn really get it, most vga cards provide tv capture right? (well mines does anyways) then why bother getting a TV tuner card? say if i only want to record tv shows and then burn them into dvds, do i really need a tv tuner card?
No and no: most VGA cards do not provide "TV capture", and, indeed, very few VGA cards provide "video capture".
A few definitions are in order.
A "VGA" card is what is commonly called a video graphics card. It processing digital graphics and images including video files from various software applications, and projects the signals to a PC monitor. Generally, it can not do TV or video capture without the presence of another device.
"Video capture" generally refers to the process of recording video from an outside analog video source like a VCR, camcorder, a game console, or some other device. Most video capture cards are on PCI cards, and are installed in a PCI slot. But, these capture devices can be found in the PCI express and USB form factors.
Let's use a VCR as an example. You put a VHS tape with a recorded video in a VCR. You connect the VCR to a PC with a video capture card, either using a composite cable or a svideo cable. With the proper PC software, you can record the VHS tape to the PC's hard drive.
A "TV tuner" is special kind of video capture device. A TV tuner for a PC is no different from the TV tuner in regular television sets, except that it is on a PCI card, a PCI express card, or in a USB card form factor. The tuner could be an analog (NSTC/PAL) TV tuner or a digital (ASTC/DVB) TV tuner, or a combo of analog and digital HD.
I would say that most brands of TV tuner cards on the market today can also provide video capture. Stated another way, most TV tuner cards have extra ports that allow you to connect a composite and/or svideo cable from a video source like a VCR for "capturing video."
On the other hand, most video capture cards are not also TV tuners. You can't pick up TV signals and watch TV on your PC monitor using a plain old video capture card because plain old video capture cards do not have TV tuners.
As most TV tuners can also capture video, a few models of TV tuner cards can not. For example, the Dvico Fusion 5 Lite is one such TV tuner that can not provide video capture. It only does TV.
As I suggested, there are a few VGA cards that can do video capture. Generally, you will know them by their specifications that say it supports VIVO (video in, video out). Many of the ATI Radeon 1X00 cards can do VIVO. So, regarless of brand, check the specs for VIVO if you want a VGA video graphics card that can also do video capture.
Then, there are the very special VGA cards by ATI called the All-In-Wonders, which are video graphics cards, TV tuner cards, and video capture cards. The AIWs do all these functions very well.
At last notice, all of the ATI AIW cards are analog TV tuners. The can't pick up HD TV signals.