It is not possible to check winds at cruise altitude in FSX.
To do that you would need a good weather engine (for example Active Sky Next). In ASN you can check weather forecast for your flight plan (you can import FSX flight plan to ASN to get the weather forecast). It will also give you your Ground Speed forecast.
Alternatively - with ASN you can check look at Skyvector.com and check wind on your altitude (show Wind Barbs option in Layers menu). From this you can calculate headwind/tailwind components in selected waypoints. You can use this calculator: http://mye6b.com/e6b.html#_Wind