At home I use 2 screens. The main screen is atached to a 3dfx Vodoo3 card and the 2:nd screeen is atached to a Matrox MGA Millenium card.
When I install SI it ask me if I whant to use the matrox card. I change the card to 3dfx and check the Universal box. Test the screen and its seems to work.
Reboot.
Press ctrl+D and SI pops up OK. The problem is that the mouse pops up a window everytime I move the mouse. (The same vindow as it you press right-mouse-button)

I look at winice.dat and see a row with monitor. This line is set to monitor=0.
The mouse is a std MS mouse attached to the PS2 port.

Reinstall of Win98se and the problem was solved

Hello JohnnyBoy !

I had this kind of problem too. But this came because the "Video Utility" didn't like to accept any company names starting with a number. So "3dfx" failed, since the "Video Utility" made some lines in the WIN.INI which where empty instead of containing the video cards name and manufracturer.