There are two ways you can boot from an SDHC device, the manual way is to hold down the Esc key when starting up the eeePC and selecting the device to boot from, but you can also have the eeePC boot from your SDHC card automatically:
Turn on the eeePC and press F2 to enter the BIOS.
In the BIOS menu, navigate to the BOOT tab.
In “Boot Device Priority” apply the following:
Once this is done, hit Esc and go into “Hard Disk Drives”
Apply the following settings in “Hard Disk Drives”:
Note: If you do not have the “Hard Disk Drives” setting, it's possible your BIOS is not one of the more recent ones, or that you do not have a SDMC or USB PenDrive plugged into your EeePC.
Note: Booting later with no SDHC card in the slot may reset the 1st boot drive to HDD:sm-siliconmoti.
Hit F10 and save your settings. Now when your eeePC boots it will boot from the card reader directly first.