Firstly a move from a Mac to a PC is not an upgrade ;) I couldn't resist - sorry.
But moving from v5 to v10 is a huge upgrade.
On your PC, you will be able to open all the v5 files in v10. FileMaker Pro will copy upgrade these files to v10 structure.
There have been issues upgrading from pre-7 to 7+ (whatever the number of versions difference). You need to check your solution carefully and ensure that all scripts run as expected. It may not be a small job.
Secondly, the visual differences between Mac and PC are greatest when you go Mac to PC. Often, the fields are slightly smaller and the labels may appear chopped off. Easiest fix for the labels is to double-click them in layout mode. Fields may need to be checked for size.
Good luck with it. Make sure you keep a backup of your original v5 files.