Install Windows 7 RC without using a DVD

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So... I installed the beta a while ago just by mounting it within Vista, and suprisingly it worked even with the restarts. For some reason, though, the new RC of windows 7 does not work by mounting. I tried copying it to a flash drive and booting from that, but the weird bootloader that came with the beta seems to be be screwing up the boot order. I select USB_HDD in my bios, but nothing happens. It just goes to the Windows Vista or Windows 7 boot screen. Any ideas on how to do it without a DVD? I don't have any and don't really wanna go buy any... but i might if there is no other way.