If your OS is Tiger Server, this should work:
Log In to the server with Workgroup Manager, click the Sharing Tab in the toolbar (yellow sign, second from left). Then click the “All” tab below, you should see the mounted Xserve RAID in the first column.
Click it and look right, the first checkbox should say “Share this item…” you’ll obviously want to click that. 🙂
Now click the Protocols tab, and select Windows File Settings. The rest should be cake.
HTH