windows through HDD and linux through USB , how ??

Hi
i have 2 PCS , the new one is ok , but the old one …
i want my old PC to work like this
install normal windows xp on the pc , but when i change my mind , i switch to linux through USB device boot

i have downloaded the ubuntu iso burnt it into cd and istalled it on the old pc
but i changed my mind , i want to install windows on the old pc and switch to linux fastly throgh the 1 Gega usb drive
my problem
i tried to boot the cd on the old pc and as i told you , it was ok
but when i tried the usb boot (which was enabled in the motherboard) it didn’t boot :spin:
i copied all iso contents to the usb drive , but it didn’t boot !

is there a special way to make the usb drive bootable ?
in this case , would 4 gb usb be more suitable ?

and my linux wouldn’t run 3d desktop , i have geforce fx 5200 :frowning:

sorry for the bad english , actually i’m from jordan
and one another reason i’m sleepy (nothing important here)
bye

in your bios, set your boot sequence something like this:

1:CD
2:USB
3:HDD

that will make it look for a bootable CD first, then a USB drive, then a Hard drive.

If you have the option, switch the USB drive to master, rather than slave. Cable select will work the same as setting it to master.

Why not just re-partition the hard drive and make it dual boot? It would be much easyer.

is it right to copy all the files of the iso to the usb ? or is there a boot sector that have to be copied too , i don’t know , …
the boot order is exactly like you have said , thanks

You do need to write a bootsector to the usb drive, google is your friend:

I agree, Google is your friend…

http://www.debuntu.org/how-to-install-ubuntu-linux-on-usb-bar