Try running XF86Setup, xconfigurator, or xf86config, and manually specifying the new video card, rather then letting something automatically detect it.
When I first ran linux on an i810 chipset, I was using RH6.2 which didn't come with an agpgart kernel module. Without agpgart, the i810 graphics chipset is crippled because it can only use something ridiculous like 512kB video RAM. I added an S3VirgeDX PCI card and had no problems. No jumpers were necessary.
Later, when I went to RH 7.1, I pulled the PCI card and reconfigured the system to use the i810. Again, no jumpers were needed.
[ January 18, 2003: Message edited by: M. O'Brien ]