There is a thread going on with Alexander Kazakov on my blog who asked me a question on how to use SQL Server in a VM from OSX using Ruby.  One change that you will need to make is the network settings for the Virtual Machine to allow the VM to be part of your local network.

The default is NAT.  Change it to Bridged (second selection).  Now the VM will be available from the host machine (OS X).  The VM will now be on your network, so make sure that its properly patched and all updates have been run.  This is really, really required if your using XP from a new install.  

This only works if your mac is on a switch or a router that is assigning an IP address. If your computer is connected directly to your DSL or Cable Modem your asking for trouble so make sure you have at least a router!!