is there is any posibility o installing hard drive in Micros WS5
 

I havent cracked one open and looked. There are other hardware platforms that are set up for either choice, such as the Glaive (about 7 years old) and the Varipos (available today). Both these are not Micros hardware platforms.

I would keep things the same and buy the best quality and largest commercial chip I could. They arent that expensive, $85 I think.

When you look at Micros, you are looking at more complex things in this. You are also suggesting installing Windows CE onto the HDD, and remember also that the CE is stored on the BIN on a CMOS.

Plus you are forgetting the biggest thing about Windows CE: Memory Addressing:: It can only address about 4GB of hard drive / memory. Please, plug ANY usb external hard drive into it, you will find the unit cant see / mount the drive.  You cant buy a 4GB hard drive now the smallest is 160 GB.

You will find going throught his learning curve is a long slow process and ultimately a waste of your time, whem you will be trying to save $80.