I've been using the Mac OS and iOS to organize my GTD system for some time now. OmniFocus is the core of my system.
But if I was forced to use a PC with an iOS device I'd try to lean on iCloud and Evernote.
Because I've gotten used to Calendar (formerly iCal) I would try to use that tool for my calendar. On the PC I would use the web version of iCloud to see my calendar (that would work, right?). I'd probably do the same for Contacts and Mail.
For action lists I would start with Evernote and use one notebook for Next Actions by context (a note for each context) and another notebook for my Projects list (a note for each project) and a third notebook for Someday/Maybe (a note for each thing).
I haven't done thorough research but it's an option.
How did you capture that thought?