There should be a bios flash utility on the asus disk that came with the mobo. If you don't have the disk then go to the asus website under the downloads section there will be a downloadable flash utility.
Here's a guide on the asus site that explains it better than I ever could: http://www.asus.com/Products/Motherboard/flash.html . A word of warning though - I just tried flashing to this bios (from 1004d), and the new bios froze whenever i entered the 'boot' section of the bios, with all sorts of graphical glitches and stuff, and wouldn't make it into windows (thank god I saved the earlier bios to disk). As far as I know, the 1005 bios doesn't support in-bios multiplier adjustments - it was supposed to, but there was no option for me (not that the bios worked anyway). Maybe the 1005a is different though, as mine was just called 1005, so you might not have these problems. At any rate, from what I've heard all versions of the 1005 bios are pretty damn buggy :-( Wouldn't it be great to have software multiplier adjustments, just like Abit?
See the other thread on the 1005b bios - I just tried it, and it seems to work fine. Might be worth it, if only for the 1mhz fsb increments - just use the Asus Update utility on the A7v cd, much easier than flashing with the floppy (but I'd still create a disk with aflash.exe and the old bios on as described on the asus site, just in case). One thing - when I unzipped the file, it appeared as a .bin file - I had to deselect 'hide file extensions for known file types' in folder options, and rename it to a7v1005b.awd - then it worked like a charm ;-)