I'm not exactly techno-savvy, but since I prefer to look at the largest possible image, I find that if I email the images to myself (directly from iphoto) I can retain the large physical size but the file size drops from more than 1MB to around 200kb when you choose that option.
After that, I then upload to photobucket and insert the links on Urban Toronto. There is an option on photobucket to quickly make clickable thumbnails.
Hope that is of some help.