Diablo 2 not working?

So i just got a new computer with windows 7 on it, and i installed diablo 2 and the expansion onto it, but when i go to click on the icon to play it a message pops up and says.

Diablo 2 has a known compatability issue with this version of Windows. For an update that is compatable with this version of windows, contact blizzard.

Then i click run program and it says make sure the diablo 2 expansion disc is still in the CD-Rom drive.

What is the problem here. It use to work on my xp version of computer .-.

Might be the wrong disc. Insert the expansion disc and press play. First, right click the expansion shortcut and set compatibility to XP, run as admin, and disable all themes. It'll work. If Vista can do it, 7 will not fumble.