AGP/VGA Card unknown, no vidcontrol possible

Dear coders,

can you please help me getting my VGA card working so I can switch to 
VESA_800x600.
This card doesn't have mode 258 (as vidcontrol -i mode tells me) but for 
example has 259, which is 800x600x8. Is it possible to instruct the mode 
directly or to change the mode for VESA_800x600 from 258 to 259?

It's a brand new AGP card with a Rage mobility on it (without any cooling).
pciconf tells me this:
none0_at_pci1:0:0: class=0x030000 card=0x00841002 chip=0x4c4d1002 rev=0x64 
hdr=0x00
    vendor   = 'ATI Technologies Inc.'
    device   = '01541014 Rage P/M Mobility AGP 2x'
    class    = display
    subclass = VGA
(none0_at_pci1:0:0: class=0x030000 card=0x00841002 chip=0x4c4d1002 rev=0x64 
hdr=0x00)

dmesg says:
agp0: <VIA 82C691 (Apollo Pro) host to PCI bridge> mem 0xf8000000-0xfbffffff 
at device 0.0 on pci0
pcib1: <ACPI PCI-PCI bridge> at device 1.0 on pci0
pcib1: could not get PCI interrupt routing table for \\_SB_.PCI0.AGP_ - 
AE_NOT_FOUND
pci1: <ACPI PCI bus> on pcib1
pcib0: no PRT entry for 0.1.INTA
pci1: <display, VGA> at device 0.0 (no driver attached)

Thanks,

-Harry