What version of Wine are you using? I downloaded the trial version of SigmaPlot 11, and it starts up fine for me with just dcom98 (installed with winetricks), and the Windows version set to Windows 98. I don't know enough about the app to really test it, but it seems to be working. I'm using Wine 1.1.4. If you're using an older version, upgrade, then try installing again to a clean wineprefix. If you're already using 1.1.4, try installing to a clean wineprefix, with only dcom98--that other stuff you installed may be what's causing the problem.
