|Check the minimum system requirements for the TV tuner card or adapter|
The better the TV tuner chipset is, the lesser the load in places on your system (your CPU) - the better it is, the more processing work the chips on the card or adapter do themselves.
If you intend to use the PVR feature (Personal Video Recorder, or sometimes called DVR - Digital Video Recorder) you need to have enough free space available on one hard drive partition or another to store as many recordings as you think you're likely to have at any one time before deleting them once you've seen the recording. .
All modern TV tuner chipsets stream the TV output - if you compare the video output to that of a TV that's on the same channel, the output from the TV tuner card or adapter is delayed slightly from what you see on the TV, the better the TV tuner chipset, the lesser the delay. Even if you don't intend on using the PVR feature to make recordings, you need at least a minimum amount of extra free space on C (or whatever drive letter of the partition Windows was loaded from - for XP or for a multiboot system that can be other than C ) to be available other than the minimum that is needed for Windows otherwise for the streaming to work properly.
Like when you use a VCR, you can Pause, Rewind, even when you haven't made a Recording, or .Pause, Rewind, or Fast Forward if you have made a Recording.
The free space for the PVR recordings doesn't necessarily need to be on the partition Windows was loaded from, but the streaming and the PVR recording prgram are often optimized such that they work best if the free space is on a NTFS partition rather than a FAT32 partition.
(If you use the drivers for Media Center for the TV tuner and use it in Media Center, at least in the XP MCE 2000x versions, when you specify the recordings are to be placed on a FAT32 partition, you get a message from Media Center that that isn't recommended.)
However, I don't recommend that you specify that recordings are to be stored on an external drive's partition - the data transfer rate to and from a external drive is probably too slow for the streaming or the playback of the recording to work properly .
TV tuner cards / adapters have one drawback - you can't watch a channel from it other than the one you're recording when you're recording it, unless the card or adapter has more than one TV tuner built into it.
There are some of them that have more than one tuner built in,. or you can install two of the same cards or adapters, or different cards or adapters that are using the same TV program.