You will need your original Classic\Expansion CD set that you use now to play Diablo II. You will also need another set of different Classic\Expan keys.
After setting up the MPQ file, you can use the second Diablo II shortcut on the desktop to load the extra keys instead of the ones you installed Diablo II with.
The D2CdKey is your second classic cd key, the D2x is your second expanssion. After replacing your D2GFX.dll with
this, editing and merging the
auto-cdkey.reg reg file, and refilling the keys in the
d2-cdkey.exe program following my instructions, you should now be able to use the two Diablo II shortcuts at the same time.
If you followed the guide, you should have
TWO shortcuts to Diablo II on the desktop, on
one of them, modify the Target in the Properties to look like this.
"*Your Diablo2 File, DO NOT CHANGE THIS*" -mpq cdkey.mpq
If you followed the directions, it should work.