One, I don't recommend a BIOS update and I never will. The reason is that if it goes wrong (worse case scenario) you will never be able to use the motherboard again without performing hardware level programming. More than likely you wouldn't have any problems however considering the risk I prefer not to do so. Granted you can usually download an ISO to burn a disk that will hypothetically restore the BIOS but if it is completely screwed up the motherboard won't be able to use your cd rom drive much less your chip set, cpu, card slots, hard drive connections, etc. You have to get the BIOS right or you will be screwed.
Second an upgrade license of 7 won't automatically activate after a clean install without either a hack or the Microsoft activation help desk allowing you to manually enter in an activation code. I have had the hack not work and the tech refused to perform the manual activation so I had to perform a clean install of Vista and upgrade 7. The problem is that you can't "upgrade" from 32-bit to 64-bit however if you explain to the Microsoft tech that you went from 32-bit to 64-bit hopefully they will be understanding and help you. None the less you will have to go through the painful experience of calling Microsoft, being put on hold, and working with them to perform activation. Just something to consider. Really without having 4 gb or more of ram you don't "need" 64-bit. Really 2 gb is decent and I have lived with it before.