windows 2000 server io performance

Does anyone know if Windows 2000 Server has a bottleneck of only being able to serve 1 IO to a lun at a time? We are running sqlserver on a 2000 server box and when I am looking at perfmon, I often many ios in the average disk queue length. Most of the literature I have read states that if you have more than 2 IOs in your disk queue length, you are probably experiencing an io bottle neck. My lun (drive) is a raid 5 set of 6 10k ultrascsi2 disks on a San. My san does not “seem” to be anywhere near taxed, that’s why I’m wondering if it is windows not being able to push to the lun.