If you don't mind me asking, what's going on in Sapporo? Is it the classical music festival?

Japan-Guide:Sapporo Travel Guide may really be all you'll need up there, unless you're planning on going hiking or to play in the mountains.

However, if you're really a vegetarian, you're not going to be able to eat the ramen up there, which is super delicious. Another good guide to Sapporo/Hokkaido is Quirky Japan: Hokkaido, which lists other items of interest and some of the onsen up there.