There should be icons on the top edge of the screen, on the right, if you are poisoned or under a spell effect. If you hit Enter to pause the game you can mouse over any icons to see what they are (basic info) and any time limit on the effect. See the 'Buffs and Debuffs' list starting on page 28 or 29 of the manual (for D2:DC or DKS, respectively).
