Man, it's only like 367 bytes or something like that. Get yourself a copy and learn assembly.
- http://www.xs4all.nl/~smit/asm01001.htm
- http://win32asm.cjb.net/
- http://cs.smith.edu/~thiebaut/ArtOfAssembly/artofasm.html
Art of Assembly is a whole free ebook on the subject. Learn that, get a copy of the worm, and disassemble it with a disassembler (read: search http://www.google.com for "disassembler"!), and you'll have a copy of the assembly level source code for the worm, and the ability to understand it.
Note though, the fact that it spreads so fast was apparently an accident, simply because it had no limit placed on it for how fast it spreads (because it was so small).

Don't go writing your own viruses and worms though, or at least if you do, keep them on your own computer/network, and don't let them get out on the internet, otherwise you can go to prison (not to mention how lame it is to intentionally spread viruses).