I got this at www.sis.com/support/driver/vga.htm and clicked on SiS5598. That leads to a page where you can select YOUR operating system. These files are for Win98.
The following files are found inside the driver download file.
|Readme.txt||160 bytes||23 Feb 2002|
|SiS55982.exe||1.4 MB||23 Feb 2002|
|597v113.exe||35.1 KB||23 Feb 2002|
|SiS55983.exe||1.3 MB||23 Feb 2002|
|SiS55981.exe||870.6 KB||23 Feb 2002|