ATI has a new product called the TV Wonder USB
Here I dont know much about it except the last time I checked it was around $100.
System Requirements
Intel® Pentium® 4/III/II, Celeron® or other USB-compliant PC
Installation software requires CD-ROM drive
Sound card
Speakers
Cable TV signal or amplified antenna
Available USB port
Iteractive Program Guide requires Internet connection
TV browser requires Microsoft® Internet Explorer 4.0 or later
Operating Systems Support
Windows® 2000
Wndows® 98
Windows® Me
Check it out, it looks like it should be what you want