You would first have to deal with anything worth saving off of the 98 drive before using something like Norton Ghost or Acronis disk imaging software. The simply way there if you are planning to use the 250gb as a stand alone is to set it as the master and perform a fresh installation of Pro. When simply cloning you don't necessarily create the master boot record and partition information when transferring to a different size and maybe brand drive.
I run two 250gb drives here with a good fresh installation on both to avoid problems that can come up with a bad clone plus a different OS on each one. A fresh detection of all hardwares especially with XP on a clean install generally sees the best results. It can be done. Businesses have this done all of the time due to having identical drives and hardwares along with the same applications. There ir is a practical time saver and a tax deduction as a business expense to have someone do it.