IMO, the multiplier option remains as a crule joke to the average consumer that can not purchase an unlocked engineering sample processor.
In reality, the multiplier range on some P4 models can sometimes we adjusted within certian tolerances, but the information is scarce. It is almost a random process in my experience.
As to overclocking, I do not believe the P4VXASD2+ supports manually setting the FSB (been awhile) with any official BIOS release. You could try CPUSOFT or similar Windows-based overclocking utility, though I am not sure any will properly recognize this board's ICS-branded PLL chip.
Seems I remember reading about someone (another forum) having to give up on overclocking the P4VXASD2+. I believe he ended up replacing the board with an Abit model.
Robert Richmond