yes, you can run ur pc without hard disk. you need a dos  
in floppy or cd

You can run a PC w/o a HDD using a BOOTP server, which 
sends the OS to the target m/c and in addition to that it 
acts as a DHCP server to provide IP address

PC without HD is a dumb terminal and boots to an image on 
the network. It could be a citrix or windows terminal 
server or better yet t could be vertual PC with a shared 
storage on a SAN type of shared storage. Current NICs have 
a cability to ask for DHCP and connect to a resource 
through the usage of bootp.

computer run without hard disk throgh cd/ pen drive & other 
bootalbe media.

yes we can run a pc without hdd by using thinclients

i never seen any computer which is runing without or with 
harddisk.

Yes, You can run computer using bootable CD, which contains
OS  in a cd this OSs are Knoppix and Chevna. it loads OS in
RAM, you can save and surf internet too until is restarted

with flash memory computer can run without hard disk.its 
proven.

this all answers are not cleared. plz answer clear.

yes we can run computer without HDD. The solution is 
ThinClient.

To Rana,Which type of system u have seen