Not a particularly helpful reply but here goes. I don't think it's got to do with vista (I expect there are some programs out there that let you do it anyway) it's do with the motherboard, I've got an M2N-MX at the moment and on the specs it says I'm able to customize the boot screen, although I've yet to find out how myself (helpful I know)
But yeah, check if it's possible on your MoBo first as I think it's more to do with that tbh. Sorry for the lack of help.