Yes we were able to get Snow Leopard Server with Parallels 5 and Win-XP Pro to host the "Quick Books Server" that comes on the QuickBooks installer CD to work quite well. Then my customer decided they did not want Windows on their Mac Server so we deleted Parallels and all Windows components.
So we tried a second approach and that was to run Parallels 5 on 3GHz iMac and host QuickBooks from there using Multi User QuickBooks setup.
We kept getting errors from Quickbooks on the 2nd machine [older 2GHz MacBook (Intel Core Duo & not Intel Core 2 Duo) running Parallels 5 and Win-XP Pro]
Our data was stored on the newer iMac in the Users/UserName/Documents/QBstuff folder. The iMac used this data with no problem. It was just the 2nd Mac running Windows that could not access the data. We even shared the mac folder and had it sitting on the old macBooks Desktop but QuickBooks just said NO!
So then I moved the QuickBooks data to a folder created by Windows inside the "C:" drive. For the most part that made it work.
It turns out our old MacBook could use data from our Snow Leopard Server but it was walking through mud when it accessed data from the iMac.
We threw in the towel for now and will just use 1 copy of QuickBooks.
We even ran a pair of new CAT 5E cables from our AirPort Extreme router to the two Macs trying to run Parallels and Quickbooks and that did not seem to make any difference.