First off, I want to say that this is completely different from other questions about putting the installation files onto flash drives (i.e. Install Windows 7 from USB flash drive and How to install Windows 8 from USB flash drive?).
Background
I have a "server" running Windows 7 Ultimate that I got from Microsoft. It has 3 IDE hard drives and 2 SATA drives. I want to move the 20GB IDE drive, which is the boot drive, onto a flash drive and boot off of that. The other IDE drives will get converted later when I get more money. The current motherboard is dying (blown capacitors, broken fan blades on CPU that seems to be custom), and needs to be replaced completely.
What is going in
I have decided on the Asus E35M1-I motherboard, for the 6 SATA ports, and the fact that it's tiny has no importance to me; it's a file server, and the other services don't require extra PCIe or PCI slots. The new motherboard I'm buying, of course, has no IDE ports (hallelujah/dammit), so it will need to move the IDE drives to SATA. But with my 20GB IDE drive, I don't see a point in buying an SSD for a simple file server, or trying to buy an adapter kit to convert SATA to IDE. So the conclusion...
The Conclusion/Question
Can I image (i.e. with Linux's dd command or Acronis TrueImage) my boot drive to a Flash Drive and have it boot the system?