Regarding version 5 above:

The changes are small enough that you should be able to just drop in the new NotifyIcon.ctl and .ctx and recomiple your existing Projects with no changes. The main "visible" change is that the BalloonShow() method returns a Boolean "success" value now where False means you're on a pre-Win2K OS. Existing programs can just ignore the result value, or be changed so they can deal with it some other way.

I haven't done a full test on all Windows versions but it tests OK on Win95 OSR2 w/Desktop Update, Vista SP2, and Win7 SP1.