All testing was done with Windows 98 SE
Network
Realtek PCIe gigabit chips RTL8111C and RTL8111D tested to work - can be found as either PCIe cards or integrated into motherboards.
RTL8111E and above don't work with the regular Windows driver, but, in theory, may work with the NDIS 2.0 DOS driver (I have not tested this).
TV Tuners
Hauppauge WinTV PVR 250/350 works (currently using driver version 1.18.21.22266 found on the WinTV PVR 2.2A CD https://archive.org/search?query=WinTV+PVR+2.2A). This card is pretty versatile and can be used with Windows Media Center in 32-bit XP/Vista and presumably Win7 as well (just not 64-bit).
Although in the same WinTV PVR product line, the 150/500 versions do not work with Win9x.
Video capture from an ATI All-in-Wonder X800 XL (PCIe) partially works in that I can capture from the S-Video port but there is no audio. Workaround: connect audio to a sound card's line-in jack instead. TV and FM tuners do not work and show a code 10 error in Device Manager - this does not impact video capture, only the tuner portion. It's better to use this card for capturing video under Windows XP but still noteworthy if you're dual-booting.