Shares of VMware (VMW) were down nearly 20% in early trading on Tuesday, at 13-month lows, after the enterprise software company late Monday forecast weaker than expected revenue for the current quarter. VMware also said restructuring will result in layoffs of 900 workers and a first-quarter charge of $90 million and $110 million. VMware is the leading provider of virtualization software, which lets companies run multiple operating systems and