Sun Microsystems ( SUNW) reached an agreement to acquire SeeBeyond ( SBYN) for $4.25 a share, valuing the deal at about $387 million including the assumption of employee stock options. SeeBeyond, a provider of business integration software based in Monrovia, Calif., had revenue of about $167 million during the last 12 months and has 2,000 customers worldwide. In premarket trading, shares of SeeBeyond were gaining 85 cents, or 26%, to $4.13. The stock's 52-week high is $4.20. Sun was adding 2 cents to $3.71. Sun said the products and services offered by the companies are complementary with little overlap. The company expects to complete the purchase this fall.