I just found the tournament website for the 24-team Palm Springs Classic, which starts tomorrow and runs through Sunday (if you go to the tourney website, you'll need to scroll down a bit to see the list of participating teams and the schedule).
Northwestern, ranked No. 2 and 3 nationally in the two major polls, will be playing in Palm Springs. So will UCLA, Arizona, Oklahoma, and LSU, all of whom are ranked in (or near) the top 10. The U.S. national team is also included in the field.
Elsewhere this weekend, consensus No. 1 Alabama will play in the Florida International University tournament.
Arizona State and Texas A&M, each of whom is in the top 4 of both national polls, are both in action this weekend. The Sun Devils host what looks to be a low-key tournament, a pattern they will be repeating for the next couple of weekends thereafter (see ASU's homepage in the links section to the right, for the team's schedule). The Aggies, too, will be hosting a tournament this weekend; similar to ASU's, the A&M tourney lacks "big name" opposition.
Given how cold February tends to be in the midwestern and northeastern United States, college softball teams from these regions typically will travel to warmer climates to play in tournaments at this time of year. In recent weeks, however, some snowbelt teams have been staying home -- and under a dome.
I've tried to find pictures online of softball being played on what ordinarily would be a baseball or football field, with some success. There's a nice photo gallery from the February 9-10 tournament at North Dakota State's Fargo Dome. For the 2007 Northern Iowa UNI-Dome Classic, I found two galleries (here and here); you might want to check back here to see if 2008 tourney photos appear at some point. Finally, Minnesota has hosted a tournament at the Metrodome in recent years; here's an article from 2005 with a photo.