Diablo 2 in a Window
Although not documented, you may run Diablo 2 in a Window instead of full-screen. Simply add "-w" to your Diablo 2 shortcut.
(ie: "C:\Diablo 2\Diablo II.exe" -w)

Retrieving Items from Dead Corpse
If you die and cannot make it back to retrieve the items from your dead body, simply save, exit, and return to the game. Your corpse will appear in town and you may retrieve your items easily.

Secret Cow Level?
In order to find the secret cow level you are going to need a few things.

1.Wirts Leg
2.Beaten the Game
3.Tome of Town Portal (with scrolls)
4.The Horadric Cube

Once you have beaten the game go to the Rogue Encampment in Act I, then put Wirts Leg and a Tome of Town Portal (This has worked with random ammounts of scrolls in the tome) into The Horadric Cube. Once you hit transmute they should disappear, but once you close your inventory window there is a red portal that will lead you to the Secret Cow Level. This ONLY works in the Rogue Encampment in Act I.

Tips:

Tip: Before selling an item, repair it. This will increase its value.

Tip: Always have several Town of Portal spells ready. These portals can provide a quick escape if the dung hits the fan and there's no other way out.

Tip: You can use the waypoints to move between the different acts. This is helpful if you want to go back and buy an item or get something repaired.

Horadric Cube formulas:

The Horadric Cube, found in Act 2, works as a kind of magical catalyst. If you put certain items into the Cube, it will transform them into another item. Here are a few formulas that work:

2 quivers of Arrows = 1 quiver of Bolts
2 quivers of Bolts = 1 quiver of Arrows
1 quiver of Arrows + 1 Spear = 1 bundle of Javelins
3 Perfect Gems + Magical Item (armor, weapon, jewelry) = random high level item
2 Topaz + 1 Ring = 1 Coral Ring (lightning resistance)
3 Mana Potions + 3 Heal Potions = 1 Rejuvenation Potion
3 Gems of same grade and type = 1 higher-graded Gem of same type
3 Rings = 1 Amulet
3 Amulets = 1 Ring

NOTE: These formulas will not work with patch 1.02 installed.