I am running FMP 8.5 clients on a variety of OSX and Windows platforms, with the actual Filemaker databases hosted on FMS 5.5 on OSX10.5.

The next Windows machine I get will have to be Windows 7, which means it will have to run FMP11. According to the FMP11 specs, "FileMaker Pro 11/Pro 11 Advanced databases use the same file format (.fp7) as FileMaker Pro 10/Pro 10 Advanced, FileMaker Pro 9/Pro 9 Advanced and FileMaker Pro 8.x/Pro 8.x Advanced therefore databases can easily be shared between these versions."

The question is, can I have a client machine running FMP11, and other client machines running 8.5, all accessing the same databases running under FMS 5.5 on OSX10.5?

Some day I will obviously have to upgrade everything, but that's a lot of cash to spend right now if I don't NEED it right now...

Thanks very much for your time.

FMS 5.5 on OS X 10.5 with FMP 8.5 clients - not possible.

FMS 5.5 hosts .fp5 files, these can only be accessed by FMP 5, 5.5 and 6.

FMS 7+ will host .fp7 files and these can only be accessed by FMP 7+.

Sadly you missed the opportunity to upgrade the 8.5 clients and FileMaker Inc have withdrawn support for them - you're pretty much into a complete re-purchase. Look at the workgroup bundles and site licensing options from FileMaker. It all depends how many you need - but whatever you do get on the maintenance program as it's a lot cheaper than re-purchasing.