How to Switch to 4X-AGP on GA7VAXP?!

Hi!

I have the following problem:

I have a GeForce 4 with AGP 8X which locks up everytime I play a game
(looks like the system is going into standby-mode). If I use a
windows-tool (powerstrip) to set the AGP-speed to 4X everything works
perfect!

Now i want to set the AGP 4X in the BIOS (so I don't need the
windows-tool), but I can't find the "AGP Mode" entry there! So I've
downloaded and flashed a hacked bios where every option should be
available (also the AGP-Mode entry) but I can't find it! (I already
used CTRL-F1 in the BIOS to show all options) - the current AGP Speed
is displayed (8X) but why is this damn AGP-Mode-entry unavailable! It
can't be!

Any ideas???