First you need to install the device using Win9x
drivers and be told that the .inf is in the wrong format. That's okay - just
click ok.
Unpack u2e304.zip into a temp folder and go to
device manager and update the driver for the 3C19250 using the "have
disk" method, and navigate to the folder where you unpacked the KLSI driver,
select it, ignore the warning about it not being the right driver for the device,
and click OK.
You now are a proud owner of a Klsi USB-Ethernet
Device Adapter!
Download drivers - http://www.klsi.com/drivers/u2e304.zip 
Step by step instructions http://www.usbman.com/3Com%20Ethernet%20Adapter.htm 

3Com never released Win2000 or WinXP drivers for the 3C19250 USB NIC. The product is also now discontinued.

You can download a KL5KUSB101 driver for Windows 2000/XP that I modified to work with the 3Com 3C19250.

Use at your own risk:
http://tenshi.virtualave.net/3c19250_xp.exe