Ok step by step:
When asked if you wish to install Windows XP press Enter.

You will be presented with the End User Licensing Agreement. Press F8 to accept and continue or press F3 to cancel the install.

Move to the Win 2000 partition and delete it.Once you've deleted partitions you will be asked to create a partition. At this point you can choose the size you wish. Most people will elect to create one partition that fills the entire drive. If you decide you would like multiple partitions then create a partition size that will be suitable for XP and your installed apps as well as room for cache files etc. 10GB is s nice size for a full XP install leaving plenty of room for applications etc. After XP is setup and running you can create additional partitions in the free space through XP's Computer Management Console.

The next screen asks if you wish to use the NTFS file system. This is the preferred file system, however, if you choose to use FAT32, you will not have all the security and stability features of Windows XP.

If you have NOT deleted the Win 2000 partition and are installing over the top you will be given a choice of Format options . Select the Format option of your choice(I'd go with NTFS and not the NTFS Quick Format). When asked to start the format, press the "F" key. The formatting process may take quite a bit of time.

Setup will begin an automated loading of files which will take several minutes.

After this is complete the computer will restart. Leave the XP CD in the drive but this time DO NOT press any key when the message it "Press any key to boot CD" is displayed. In 5 seconds setup will continue.

The Windows XP Setup wizard will lead you through the process of gathering information about you and your computer.

And that is pretty much it done. Remember to DELETE the Win 2000 partition and create a new one, or at least format it before you try and install XP.

And the most important thing is to backup everything you want to keep onto DVD or CD as deleting or formatting the partition will erase all the information stored on it.