Umm where did you get your information? XP Pro is NOT required. From a programming standpoint, XP Home and XP Pro are virtually the same. According to Microsoft, PDH is supported in NT4/2k/XP/2003. So Where you came to the conclusion XP Pro is required is beyond me.
Secondly, who cares that people use 98? 95/98/ME/NT4 don't support transparency, but guess what? mIRC does. Why? Because Microsoft isn't totally stupid, they made it so you can work with features that are not available in all versions of Windows while still allowing compatibility. So what happens if someone is using Windows 98? They can't take advantage of the new feature.
To be honest, your post made me laugh. When I read the thing about win98 the first thing that came to mind was, a quote I once heard. "If you can't solve all the World's problems, don't bother solving any." That's a ridiculous assertion. Yeah, so we can't fix the problem for Win98 users, does that mean we shouldn't fix it for the NT4/2k/XP/2003 users? It's foolish to say that we shouldn't.
