|"i have no disk or floppy drive from which i could stick a boot cd into, so can i boot dos from a flashdrive or what."|
What is the size of the hard drive ?
If it's greater than 137gb, or if it's a SATA drive, there are additional things you need to be made aware of.
As Richard59 has said,
"....you cannot take a hard-drive with XP installed on it and transplant it into a different hardware environment. At the very least you need to do a repair install..."
.....as in, a Repair installation of Windows procedure - I recommend that if the hard drive has a lot more than just what was installed by Setup on it - for that you need to connect an internal optical (CD or combo CD/DVD drive) drive to the same computer.
In any case, you need an XP CD to fix your problem, preferably of the same version - Home or Pro (that must be the same for a Repair installation) - that's been installed on the hard drive, and a Product Key for it that's not being used by anyone else.
Even if you can set your bios Boot Order or similar settings to boot from a USB drive, the XP CD cannot recognize most of, if not all, USB optical drive models, so that's probably not going to work, and it can't recognize any USB flash drive during the initial stages of loading files from the CD - a USB flash drive has to be made bootable a well. It can't recognize most models of USB floppy drives, unless they were available when XP was first released, circa 2001, and the only thing you can do with a floppy drive is to load the 6 floppy set that loads the same initial files that the CD normally loads - you still need a Windows CD.
There is a method of installing XP from scratch when you can't use an optical drive, but you still need an XP CD, and you need to be able to connect the hard drive, one way or another, to another computer with a working operating system, and that system must have a working optical drive.