|"It has windows XP installed already"|
That's at least part of your problem. You can't swap XP from one machine to another.
"there are no jumpers on the drive"
It doesn't mean there's not supposed to be. If you want help, you need to post your system specs & be as specific as possible. And I guarantee that you're NOT using an "AMD P4 motherboard" because the P4 is NOT supported by AMD. Try filling in the blanks:
make/model/clock speed/FSB of CPU = _________
make/model of motherboard = _________
amount/type/speed of RAM = ________
make/model of graphics = ________ (onboard or card?)
make/model of hard drive = ________
make/model/wattage of power supply = _________
power amperage specs = +3.3v @ _____, +5V @ _____, +12v @ _____
How many IDE devices do you have altogether? _____
Are there any other devices (CD, DVD, 2nd hard drive) sharing the IDE cable with the 20GB hard drive? _____