He began his career in Swedish Elite League with Färjestads BK and Swedish World Junior Championship teams. In the 1998 Entry Draft, Berglund became the New Jersey Devils's third choice, being chosen in the second round as the 37th overall pick. He continued to play for Färjestad until 2001, when he signed with the Devils. He played in the minor league Albany River Rats, the Devils' affiliated team, but began playing for the Devils themselves later that season. On 1 March 2004, he and teammate Victor Uchevatov were traded to the Florida Panthers in exchange for Viktor Kozlov.