AFAIK, any of the mobile gForce nVidia chips should meet your needs for Amithlon, Win2k, and Linux. And since UAE/AmigaForever utilizes the host OS's video driver you should have no problem using UAE/AF under Win2k or Linux. There's even a 68k version of UAE out there you may be able to run under Amithlon... Can anybody confirm this?
You can still obtain copies of Win2k from most vendors (i.e. Dell). You may have to purchase a retail copy and/or install it yourself (depending the OEM and their license). But if you're going to go with any MS OS, Win2k is the way to go.
FYI, Amiga Forver is just a commercial distro of UAE with licenced copies of Amiga OS (incl. Kickstart ROMs) 1.3-3.1 or 1.0-3.1 and a range of other extras (depending on whether you get the "Online" or "CD" edition). For more on UAE/AF, take a look at these sites:
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