Acer Inc.'s San Jose-based America Corp. unit introduced its first workstation, becoming the latest entrant in the market for high-end computers dominated by Sun Microsystems Inc. The AcerPower Graphics Workstation will run on Intel Corp.'s Pentium Pro chips and Microsoft Corp.'s Windows NT operating system. It is expected to cost $7,500. Compaq Computer Corp., the world's No. 1 personal computer maker, two weeks ago unveiled a line of workstations using Pentium chips and Windows NT. Hewlett-Packard Co. entered the market in August with similar machines, which challenge Sun's market dominance. The machines from Acer, the world's eighth-largest PC maker, will use a graphics accelerator chip from Diamond Multimedia Systems Inc.