Not wishing to be too contrarian, but you might be better off porting your Fortran environment to a more up-to-date compiler. Unfortunately I have no direct experience with the current Fortran compilers (although I've successfully used the Open Watcom C compiler for many years, I suspect their Fortran being 77 only will not suit you - it does successfully compile an old version of Dungeon/Zork that I'd been carrying around since the mid 80s!!) but I believe there is a current Gnu Fortran compiler which has a Windows version.
My reason for suggesting that that might be the better medium to long-term route is simply that as time goes on it may become harder and harder to set things up to run environments that will cope with 16-bit code. Microsoft provided Virtual XP mode as a way of helping people upgrade from XP to Windows 7, no more and no less. They junked the support in Windows 8, albeit that it was replaced by the much more flexible and arguably far superior Hyper-V and offered no obvious mechanism to migrate virtual machines from the Virtual PC built in to Windows 7 to Hyper-V in Windows 8. On that basis, assuming that you're not intending to stay on Windows 7 forever (which might be a viable option, although MS would like you to believe that XP mode is just as vulnerable as Windows XP itself now that the OS is no longer receiving updates) then Virtual PC/Virtual XP mode is a dead-end. It has one big advantage, in that you don't need to have a separate Windows XP license. Beyond that, I'm not sure that I'd go there. Your alternative, if you happen to have a valid XP license lying around, is to set up a suitable VM for VMware Player or Oracle Virtualbox (or any other freeware virtual environment of your choice, although sadly not Hyper-V since there is no version that supports Windows 7 as a host), both of which will allow you to create a virtual machine that ought to be portable in future.
Fortran 95 is good enough for 99% of what most people need
A statement that you could make about pretty much any language. Any programming language that you already know is going to be more productive and useful than one you don't but sometimes it is necessary to learn a new language because of the environments in which it is supported. Anything that I can do in PHP can almost certainly be done equally well in REXX, a language that I've been using since the mid-80s and which I can write, debug and test far more quickly than any other - but PHP is far more widely supported for web development and integrates far more easily into the related environments, so it made sense to learn it for such work rather than trying to shoe-horn in something that I knew better.