Microsoft and IRCTC have jointly launched Official IRCTC App for Windows 8 that will run on Windows smartphones, Tablets as well as Windows 8 based PCs also.
The IRCTC app for Windows devices can be used to make enquires about the trains and book the seat. The app can also be used for checking PNR status and for viewing the booking/cancellation history. The app can apparently be used to plan the entire travel.
You can download this app for free from the Windows Store.