I've got a lab with Entrega USB-to-Serial converters (AN2135SC chips) talking to PLCs on automated machinery.
We recently did a (policy-driven) upgrade to XP from Win98. Entrega's kaput, Xircom's poofed, and none of the driver files available from Intel will work on XP! They explicitly only support 95, 98, 2000, and NT4.0 (HELP!) They report 'unstable' when installed, and disable themselves.
Anyone got a good driver for that device (or maybe a generic 2135 driver) for XP?