Fred Brussel's men's squash team had the best season in the program's history, winning 17 of 21 regular season matches and advancing to the B flight of the NCAA tournament.     Colby ended the regular season ranked 13th, the highest ever, and was named by coaches as the nation's most improved team. Brussel said the squad met nearly every preseason goal, including reaching the B flight for the first time. "The B flight is sort of like the Division II competition within the tournament," Brussel said. "Essentially, it's the best eight teams outside of the Ivies."     Among its 17 victories were first-ever wins over Cornell, Frankin & Marshall, Navy and Rochester. The Mules were 8-1 in NESCAC play and won the CBB.     Freshman Mike Natenshon, the team's Most Valuable Player, shared Rookie of the Year honors with Preston Amos '01. Senior Geoff Bennett received the Scholar-Athlete Award at the national tournament.     "There won't be many schools taking us lightly after this season," Brussel said. "From this point on we will go to matches knowing that everyone will be looking to knock us off our spot."