Have you tried QuickBooks on-line version?
I have a friend who is currently using Quickbooks Pro 2008 (multi-user) on her Windows PC (which she is going to stop using), as the only user so far. She wanted her employees to be able to share Quickbooks with her so she bought 3 Macs (2 of them are minis) instead of buying more PCs because she was afraid of getting viruses. She cannot use this version of Quickbooks on her Macs because it will not convert over smoothly and Quickbooks for Macs are single-users only. To solve this problem, I installed Parallels Desktop 5 to run Windows virtually - however, this also opens up viruses (which she wanted to avoid but was the only logical way to use Quickbooks).
I'm thinking, in order for her and her employees to simultaneously use Quickbooks, I will need to install it on a file server, correct? If so, how do I go about doing that - would I she need to buy a server or can we use the PC that it is currently installed on as the server? If I am to use the current PC, would I need to buy a Windows server OS?
Also, the Macs are not networked together (other than being wirelessly connected on a router for Internet access) along with other computers that belong to her sister. Any suggestions on this, too?