Thanks Ken for your suggestion using diskpart. I needed this to do a firmware update to an old Sharp Aquos tv (it would recognize the update, but when it tried to flash it couldn't find it). After converting my 8GB USB to a 512 mb FAT disk, it updated fine.
For anyone who only needs to do this temporarily, here are the steps that worked for me to get it back to its original size. Note that basically I left the size variable off. I also knew I wanted to format it as fat32, but I'm suspicious if you leave off the fs part, it will format it appropriately.
DISKPART> list disk
Disk ### Status Size Free Dyn Gpt
-------- ------------- ------- ------- --- ---
Disk 0 Online 223 GB 0 B
Disk 1 Online 7657 MB 0 B
DISKPART> select disk 1
Disk 1 is now the selected disk.
DISKPART> list part
Partition ### Type Size Offset
------------- ---------------- ------- -------
Partition 1 Primary 512 MB 1024 KB
DISKPART> clean
DiskPart succeeded in cleaning the disk.
DISKPART> create part primary
DiskPart succeeded in creating the specified partition.
DISKPART> active
DiskPart marked the current partition as active.
DISKPART> format fs=fat32 quick
100 percent completed
DiskPart successfully formatted the volume.
DISKPART> assign
DiskPart successfully assigned the drive letter or mount point.
DISKPART>
one tip that may solve your problem is dat the filename (the rom) must have the name of youre model. For Example, i have an eeepc 901 so the rom must be renamed to 901.rom – None – 2015-08-19T20:46:31.330
2That is an awful restriction on that BIOS flash, yeesh. I'd write them a letter... – Shinrai – 2010-10-22T15:16:51.650
1Ken's method works. However the uncooperative Asus bios updater still couldn't read it. I solved my problem by creating a "make MS-DOS bootable" USB stick and using the AFUDOS utility. AFUDOS updated the BIOS in a jiff. – William C – 2010-10-25T03:52:59.503