Most such software lets the user choose which format and quality settings to use. Such typically increases the recording size and requires greater processing power, which may cause the real-time display to become choppy at points depending on your hardware configuration, but it's usually doable. You can also try using a third-party recoding package, such as MythTV or BeyondTV. Aside from that, consider your graphics card, monitor, hardware configuration, and current resolution settingsall of which affect the quality of the playback. If in doubt, post the details here.
I record a lot of shows and movies on my computer, but the quality is usually extremely poor. I know a big part of this is that my tv tuner simply can't compete with a regular tv. Is there anyway, short of buying a better tv tuner, to improve the quality though?