>We have NT 4 with hardware raid implemented (Stripe Set With Parity).
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>We are thinking of implementing stripe set without parity to increase the read/write performance.
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>can stripe set without parity coexist with hardware raid5?

It depends on the implementation - if you want the hardware RAID controller to do it for you, you'll have to check their manuals. You can have a hardware RAID controller managing a RAID 5 array, and then have a separate stripe set without parity run in software at the same time. What hardware RAID solution are you using? I've implemented RAID 0 (stripe set w/o parity) and RAID 5 on separate arrays under the control of an Adaptec RAIDPort controller (a dual channel 7895 chipset and the ARO1130CA, equivalent to the Adaptec 133 HA) without problem.

What is the current hardware and software configuation, and what do you expect the stipe set to buy you that the existing RAID 5 array does not?

Before giving up the reliability of the RAID 5 array, I'd want to make certain that increased bandwidth from a stripe set without parity will get you the performance you need. You might do just as well adding another drive to the RAID 5 array, especially if you RAID controller takes over the burden of managing the RAID array now, and you'd have to get the system CPU to manage the software-based stripe set. If the RAID controller is providing additional cache and management, you may well notice a drop in server responsiveness adding software-controlled stripe sets.