Hi,
WinXP guest is unable to find drivers for the video adaptor with -vga std and this vgabios.bin, not even its "standard VGA" fallback driver. The device in question is detected as "Other devices / Video controller (VGA compat.)", and its identification looks like:
PCI\VEN_1234&DEV_1111&SUBSYS_11001AF4&REV_00\3&13C0B0C5&0&10
You'll need to build multiple times with different configurations to get the pci ids right for the various vga variants emulated by qemu. I'll have some build scripts to do that here, just need to rebase and polish them, I'll post the bits ASAP.
cheers, Gerd