I think you should wait until a loader is released with proper keys .. I used VistaLoader with windows vista and it works like a charm.
Am using the same board and its perfectly safe to use the bios mod on this one as this board already has 2 bios chips (one for backup). And yes you will have to reflash the bios with the modded bios
I also have this board with an OEM SLIC. Had no problems activating Vista, but now you need the 2.1 SLIC if I'm not mistaken. There is no ASUS 2.1 SLIC's available yet. Maybe in the coming weeks/months. You will need to use a Dell or HP for now. I think I seen them around here somewhere. As for the key, I don't know if they are available either.
No problems to integrate slic 2.0 or 2.1 in bios on recents Asus mainboards ... i have both P5Q DLX and P5E with a 2.0 Slic table ... no problem with activation of vista ultimate or premium before ... Waiting for testing asus slic 2.1 when oem keys and certs should be available for win 7 ... Just for "fun" because now i have suscribed to a msdn account for three years.
There will be no other SLIC2.1 you have to wait for. Worst case will be that M$ will disable the Vista certificates, but you simply may use a W7 certificate instead of. Btw: W7 will be never cracked, it's impossible to crack, since m$ update will notice about...