Windows 2000 supports 48 pixel icons. So does Me and 98. I'm almost sure that even an upgraded Win95 can use them (can't remember what upgrade, it's been so long... Maybe Plus Pack and/or new IE).

If you really wanted to, you could have something even bigger than 48 (not really a standard icon) in Win2K and XP, but now you're getting into a lot more custom work/code.

I'll say it again... Don't forget to include a 128 pixel version for the Mac binary (along with a 32 pixel and 16 pixel version in the resource for OS 9)

Bruno