Forget about Courtney Love and Marilyn Manson: The season's most amusing pop-music feud could be Geri versus Garth. Former Spice Girl Geri Halliwell just unveiled her new logo, a lowercase g with a halo. Problem is, the design is surprisingly similar to Garth Brooks' official symbol. And a g feud is not as unlikely as it might seem. After all, Brooks got into legal wrangles last year with rapper Warren G. over use of the letter (the cases were settled). Further complicating the situation: Brooks and Halliwell are both signed to Capitol, which is in no hurry to irk its stars. For now, the label doesn't see a problem. ''Geri's logo is unique and stands on its own as a graphic image and a symbol of the artist,'' insists Halliwell's Capitol rep. But does Brooks see a g war brewing? ''You're creating a situation that doesn't exist,'' snaps Brooks' publicist. To which the only possible response is, Gee...