I found this on Canon's website.
Instructions for sharing Pixma 450 and similar printers It shows how to share from xp home to xp home, professional, vista. XP Home starts about 1/3 the way down the page.
If both computers can get on the internet at the same time, then these instructions should work. caution that windows firewall may need to be modified to accomplish this.
If you have problems, let me know.
Oops, link didnt work. on the page that shows up, there is a search box 1/2 the way down. type in "share printer" on the results page, it should be solution #2