Jay Zager, executive vice president and CFO of Gerber Scientific in South Windsor, will step down next month to assume the same position at 3Com Corp., a networking equipment and software maker in Marlborough, Mass. Zager, a graduate of MIT’s Sloan School of Management and the CFO at Gerber since February 2005, played a key role in helping the company strengthen its financial performance, improve its balance sheet and grow its presence in Asia. Gerber, which makes software and manufacturing systems for sign and graphics makers, apparel and materials companies and opthamalic lens builders, said it’s already searching for a replacement.