You can edit in either. You probably shot in 24pA, which has a 2:3:3:2 pulldown cadence that makes creating a 24p sequence easier. I use 24p sequences most of the time, especially for web stuff, but you can just manually create a 29.97 (NTSC DV) sequence and use that.
What you may have to do, first, is to right-click the footage, go to Modify > Interpret Footage, and uncheck the Remove 24p Pulldown box. That will treat the clips as 29.97; you should be able to do the drag to the New Item button routine then.
Unless you need to include some genuine 30i footage, I'd leave things as they are and just edit at 24p.