WITH THE TWINS SEARCHING FOR A NEW STADIUM AND THE VIKINGS LOOKING FOR A NEW OWNER, MINNESOTANS HAVE HEARD PLENTY IN RECENT MONTHS ABOUT THE TRIBULATIONS OF PRO SPORTS OWNERSHIP. BUT THERE ARE STILL SOME FOR WHOM THE PLEASURES OF OWNING A TEAM OUTWEIGH THE PROBLEMS. MINOR LEAGUE BASEBALL TEAMS IN THE NORTHERN LEAGUE OPEN THEIR SEASON TONIGHT (THURS) AT SITES INCLUDING DULUTH AND FARGO. MINNESOTA PUBLIC RADIO'S WILLIAM WILCOXEN REPORTS SOME NORTHERN LEAGUE OWNERS SAY THEY'RE HAPPIER IN THE THEIR LEAGUE THAN THEY WOULD BE IN THE MAJORS... SINCE THE NORTHERN LEAGUE WAS ESTABLISHED SIX YEARS AGO, ITS EXECUTIVES HAVE EMPHASIZED THAT HAVING FUN IS THE LEAGUE'S PRIORITY. THE EIGHT TEAMS NOT ONLY PLA