Of all the Iraq and Afghanistan war vets running for Congress this year as Democrats, none has a higher profile than Tammy Duckworth, who lost both legs when her helicopter was shot down in Iraq. Duckworth won a tough primary with fundraising help from Sens. Hillary Rodham Clinton and John Kerry. In a district held for 32 years by Republican icon Henry Hyde, Duckworth's military credentials could neutralize the GOP's traditional national-security advantage. But Republican opponent Peter Roskam, a state senator, is trying to woo traditional Democratic voters, picking up a Teamsters endorsement and showcasing his environmental record. In Illinois's prosperous suburban Sixth District, both candidates are playing to the middle