Thank you for your post.
The earliest version of FileMaker Pro I can locate is FileMaker Pro 6. Therefore, I can't give you a reply based upon FileMaker Pro 4.
Since this is working on other computers, can you tell me are they also running Windows XP?
Try running msconfig, and hide all Microsoft Services. Reboot and try again. Does this help?
Try taking one of the good machines on the network and switch it out with the current machine. If it is slow, then it could be a network configuration issue.
Keep me posted with your progress.