seagate expansion 1tb usb

i hope this is in the right place. 1 i need advice 2 i need help please. i've got a 1tb seagate usb sata and what i want to do is partition the hd and put windows 7 on it this is what i've got at the minute.
windows xp pro
in1t1gnrkbx 2gb ddr 333 05-51-93 of ram
motherboard p55800-vm\s
150gb hd with xp on it.
i need to format the usb drive because its got some stuff on it so what can i use to format it ?
i have x17-58996 windows 7 plus rufus v1.3.2 and dazs window loader. what i want to do is put windows 7 on the seagate and then be able to switch from xp to 7 and from 7 to xp i cannot put the harddrive in the tower thats why im going usb way if i can. i hope i've explained it right what i want to do. so can some1 please tell me how to do it please. i think ive got what i need if not what do i need i've tried to format the hd but it would not let me because it said it was in use but it was not.so can some1 tell me how to do it please. and if i have the wrong things what do i need if some1 can point me in the right direction i hope what i've put that some1 can understand what i want to do.

thank you.

 

You cannot create a dual boot where one of the OSs is on a USB drive. You need to add a second internal drive or partition the existing one.

 

thanks earlthling i'm here again. i'm not sure but i don't have room to put a second drive in the tower but i was lead to beleive that if the usb was for matted to nfts i think it is then windows 7 could be put on it then switch from xp to 7 either thru boot system or scroll lock ive put pic with post i dont if the seagate sata can go in there there is 2 sata plugins on the motherboard and my psu as sata on it to connect sata drive thanks.

 

don't know what happened to pic but i've tried again t o upload it

 

If you can't add a second hdd, and the existing one doesn't have enough spare capacity then your best option is to clone or image your existing hdd to a larger one and then partition it.