I noticed that even if you don't use dstribution/installation systems, if you only use the standard controls the apps made with VB6 are always compatible in all Windows based platforms at least from win98,2000,XP and Vista. (I know because I make my apps with XP and give them to friends who use Vista or Win98 WITHOUT using installators/setups)

But what if you use a lot of APIs ? Are APIs sensitive to different Windows editions ?
Are there some APIs that work for XP that might not work under Vista or W7 ?

Just wondering
Thanks.