What is the difference between pseudo ephedrine hydrochloride & pseudo ephedrine sulfate?

Same medicine: These are essentially equivalent. It depends on whether the Pseudoephedrine itself, which is an alkali, was stabilized with hydrochloric or sulfuric acid. Both are quite safe.

None: Both are systemic nasal decongestants. They are different forms (actually, different salts) of the same drug. They have different molecular weights. Pseudoephedrine hydrochloride is sold under the brand name sudafed. I'm not sure if the sulfate form is available anymore. For details, see: http://www.Drugs.Com/mmx/pseudoephedrine-sulfate.Html.