May be this help http://www.xfree86.org/~dawes/845driver.html

Visit http://www.sun.com/bigadmin/hcl/ to see if your h/w listed here or not.

Also you need to update BIOS so that it works

I have installed it using http://www.tools.de/solaris/xf86/ this url. You need XFree86 porting toolkit it almost supports all of your driver.