In theory, yes it should be possible as an SD card reader is interfaced via a USB port, either internally or externally. Check your motherboard manual and the BIOS settings to see if you can select a USB device there as a boot device. You will, of course need to use an SDHC card of at least 4 GB in capacity. I am going to pose this question here: http://www.vistax64.com/tutorials/181538-usb-bootable-vista-installation-flash-thumb-drive.html to see what Shawn makes of the idea.
4 x 4GB DDR3-1600 Corsair Vengeance CMZ8GX3M2A1600C9B (16GB)
Graphics card(s)
MSI GeForce GTX770 Gaming OC 2GB
Sound Card
Realtek High Definition on board solution (ALC 898)
Monitor(s) Displays
ViewSonic VA1912w Widescreen
Screen Resolution
1440x900
Hard Drives
OCZ Agility 3 120GB SATA III x2 (RAID 0)
Samsung HD501LJ 500GB SATA II x2
Hitachi HDS721010CLA332 1TB SATA II
Iomega 1.5TB Ext USB 2.0
WD 2.0TB Ext USB 3.0
If it is plugged in to the computer with an OS on it, then you can boot off it. I have not tried this, but as you can boot from a flash, then you should be able to.
My system has the option too boot from USB CD-ROM/ USB Floppy/USB SuperDisk/ Notebook Multibay/ Notebook HDD /Network ... what does super disk and that cd-rom/floppy mean?
When i plug in my USB key it automatically populates the boot menu to include the usb...