In my opinion, four drives in RAID 6 is too few; the performance will be disappointing. If you explain why you want RAID 6 (speed, data protection, increased size, bragging rights) someone here may be able to confirm that that is a good configuration, or suggest a better one. But that setup will work.
The RAID array is usually built at the chipset level, with Win7 not being aware of it. I was not quite sure, given your subject line, if you intended to build the RAID with Win7 tools or the chipset.
Finally, the obligatory advice: RAID is no substitute for backups; even RAID arrays should be backed up.
EDIT: For some rare motherboard and BIOS combinations, you may have to rebuild the OS drive if it was installed with the port drivers set to AHCI instead of RAID (and always if it was set to IDE). Dell motherboards are infamous for this issue. What sort of motherboard or prebuilt system do you have?