ohhhhh boy
this can be deep >>>>>>
IDE drive has a flat two inch wide data cable >>>ide drives have jumpers
Sata drive has 1/2 wide data cable >>>> sata drives dont use jumpers
your situation could be two things
A) right now when you boot with the 30 gig drive ....do you get a boot menu that allows options to boot into the older windows or windows 7 ?????????
if yes, then your windows boot loader resides on your 30gig drive ......which means when you remove the 30 gig from the system . the windows 7 OS has no "eyes" its bootloader has been kidnapped = no boot
to fix that you would need to perform some "fix boot" recovery console action which I am not sure how or if there is a recovery console with win 7 ?????? I know with vista they make a bootable rescue CD to fix such issues
another option you may want to explore is changing the boot order in the bios of your current computer to see if you can get the win 7 drive to boot first and then unplug the cable from the old 30 gig drive and try booting again ....... will the win 7 drive boot withouth the help of the 30 gig drive ?
we mind as well keep stirring this deep mud for you and tell you when you transplant that 30 gig drive into the new computer .......you will need to perform a win xp repair install to remove all the system drives which were in use by your old machine ...... after the repair install is done .....you will need to install all the drivers needed by the new computer system
http://www.michaelstevenstech.com/XP...install.htm#RI
you totally confused yet ?
far easier would be jsut wipe the drives clean with killdisk and install them into their respective machines and perform a clean install of each OS again