Yes, that link will help you. To dual boot, you need both operating systems installed on the same physical disk (If I recall correctly, thats what I was told in my A+ OS class, but there are probably some workarounds (like the BIOS thing))
But working off of that assumption, what you need to do is partition the hard drive (like the tutorial shows) into two. Install XP on the newly formed logical drive (probably will be E

(which is still part of the original C: drive. BIOS sees it as one drive, thus it tries to boot from the disk, and hits two options, giving the user the choice. The OS' see two drives, however. If I recall how this whole thing works). Thats all there is to it!
I installed XP first on my machine. It was a lot easier. But this can be done! Don't worry!
If you have any problems, feel free to ask more questions!
Best of luck!
--The Comodore