i am installing win 7 64 bit onto my computer. trying to do a clean install from vista 32 bit version. my problem lies in that the original DVD drive is dead and i have an external one... but it seems that the bios will not recognize the external DVD drive as a bootable drive. i've already updated my bios to no avail. is there a way to boot to a flash drive so i can wipe the hard drive? would MS-DOS work?

If your external drive is connected by USB you need to set your BIOS to accept USB connected devices as bootable. If your BIOS has a boot selection option - usually by pressing F11 or F12 at boot: there will be a prompt at the BIOS splash screen - you can select the external drive as the boot device. Until you have set your BIOS to accept USB devices as bootable neither the external drive nor a USB stick will be bootable.

there is no option for USB disk drives

Have you tried a bootable flash drive? http://technet.microsoft.com/en-us/magazine/dd535816.aspx (It's simple if the drive is formatted as FAT32.) It has the side effect of completing the installation much faster than from a DVD, even using a slow, cheap flash drive.

there is no option for USB disk drives Is there an option for "Bootable add-in cards" or similar? For anything other than IDE or SATA drives - look at the available options when you attempt to change the boot order in the BIOS?