It works starting xawtv with this arguments:
$ xawtv -noxv -nodga
blue@pandora:~$ lspci
0000:00:00.0 Host bridge: VIA Technologies, Inc. VT8375 [KM266/KL266] Host Bridge
0000:00:01.0 PCI bridge: VIA Technologies, Inc. VT8633 [Apollo Pro266 AGP]
0000:00:0a.0 Multimedia video controller: Brooktree Corporation Bt878 Video Capture (rev 11)
0000:00:0a.1 Multimedia controller: Brooktree Corporation Bt878 Audio Capture (rev 11)
0000:00:0b.0 Ethernet controller: Realtek Semiconductor Co., Ltd. RTL-8139/8139C/8139C+ (rev 10)
0000:00:0c.0 FireWire (IEEE 1394): VIA Technologies, Inc. IEEE 1394 Host Controller (rev 46)
0000:00:10.0 USB Controller: VIA Technologies, Inc. VT82xxxxx UHCI USB 1.1 Controller (rev 80)
0000:00:10.1 USB Controller: VIA Technologies, Inc. VT82xxxxx UHCI USB 1.1 Controller (rev 80)
0000:00:10.2 USB Controller: VIA Technologies, Inc. VT82xxxxx UHCI USB 1.1 Controller (rev 80)
0000:00:10.3 USB Controller: VIA Technologies, Inc. USB 2.0 (rev 82)
0000:00:11.0 ISA bridge: VIA Technologies, Inc. VT8235 ISA Bridge
0000:00:11.1 IDE interface: VIA Technologies, Inc. VT82C586A/B/VT82C686/A/B/VT823x/A/C PIPC Bus Master IDE (rev 06)
0000:00:11.5 Multimedia audio controller: VIA Technologies, Inc. VT8233/A/8235/8237 AC97 Audio Controller (rev 50)
0000:01:00.0 VGA compatible controller: nVidia Corporation NV34 [GeForce FX 5200] (rev a1)
I can't reproduce this on Ubuntu 7.04 with built-in nvidia drivers (GeForce4 MX 440 AGP 8x card) and Xawtv 3.95.
Does Xawtv produce any error messages if run in a console? Can you specify which version of Ubuntu and Xawtv are you using? Have you downloaded your nvidia drivers from nVidia web page or from Ubuntu repositories?
Thank you!