Windows XP is cool. But, it has had a program hang problem since RC2. Sometimes, programs will hang causing the computer to come to a stop. What you do is Ctrl+Alt+Delete. Then click processes and find stuff that shouldn't be running like AcroTray, AOL, etc...Kill each of these until it works. DO NOT kill tskmgr, svchost, or explorer.
Now, you can also easily do dual boot. It would be preferable that you install Windows 98, then install Windows XP.
If you do not mind loosing your data, do this:
Repartition (not using XP) your hard drive with 4 primary partitions.
1-FAT16 w/ 256 MB
1-FAT32 w/ 5 GB (5,120 MB)
1-NTFS w/ 10 GB (10,240 MB)
1-FAT32 w/ The remainder
Of course this is assuming you have 60 GB.
Install DOS on the FAT16 Partition.
Install Windows 98 on the smaller FAT32 Partition
Install Windows XP on the NTFS Partition
Install System Commander on the FAT16 Partition
Enjoy.
You now have a system w/ both Windows 98 and XP.
You can also simply reformat the HD as FAT32 and install Windows 98. Then, install Windows XP in a different directory.
As far as the Athlon XP issue. I haven't dealt with these, but some of the older Athlons came in 200 or 266 MHz. These are actually doubled 100 or 133 MHz. So, if your system has a 200 MHz Front Side Bus, then you set it for 100 MHz.