You can log on to the site right now with your login info from last year -
OSU email (with @
osu.edu on the end) and your old password. Don't know if they'll change that before 10 a.m. tomorrow or not.
Also, no word yet on groups. It doesn't look like there's a way to create anything in the Ticketmaster site. My advice would be to worry about getting tickets first; you can always create a group later, but if they sell out of a particular (ahem) game tomorrow and you waited to order tickets until your group gets its act together, you're up a creek without a paddle.