I own two HDs, the one with Win2k installed and the other with Win98. Is it worth to upgrade the second HD from Win98 (First Edition) to WinME ? I only use Win98 to play games and watch DVD movies. In games will the performance be increased? Will I have any gains from that upgrade?

No! Don't do it. I installed Windows Millennium on my other computer (older Pentium II 32MB Ram) and have later determined that drivers for Sidewinders pro 3d and voodoo 2 are missing

WinME RULEZ. It is the best of the Windowses based on the old code. Not as good as 2000 but all the drivers forn 98 work on ME. (Unless u can prove otherwise)
Try it