If you're asking for native gameport support on Vista or later, you're pretty screwed if you're using a 64-bit OS. 32-bit driver workarounds exist, but I've never tried them since I don't see a point in running post-Vista Windows on non-64-bit machines.
As for gameport-to-USB adapters, the ones I've used just plain suck. Low axis resolution, won't hold calibration, jitter, only work with analog gameport sticks (so forget about Microsoft SideWinder or Logitech ADI hardware) etc. You're much better off breaking out the soldering iron and learning how to solder all your pots, buttons and switches to a new USB controller board.
There's a reason you need a 3DP-Vert adapter for proper SideWinder 3D Pro and 3D Pro Plus/first-revision Precision Pro support (before the second-revision Precision Pro added a native USB interface and a pin adapter). You won't get all four axes and the extra four base buttons without it. (On the flip side, the 3D Pro's TM FCS/CH Flightstick Pro emulation is what makes it actually usable in DOS.)
You have additional complications if it's keyboard port-programmed gear like the TM F-16 FLCS/F-22 Pro, because that stuff can't be programmed through XP or later. Gotta boot up DOS or Win9x and do your programming there.
Personally, unless your gameport-era gear's a really elaborate HOTAS setup, I don't even see the point in trying to convert it for modern computer usage. You can buy new TM T.16000-M sticks for $25 these days with far better precision and a modern USB interface compared to most gameport-era gear, and if you're looking to step up to HOTAS, second hand Saitek X-45s are cheap!