Is it permissible for a person to lend a sum of money and ask the borrower to purchase a specific item for him when he has the money available, and does this fall under the category of usury (riba)?

The lender's condition that you purchase a car for him with the loan amount makes it unlawful interest (riba), because it is a benefit for the lender that he stipulated due to the loan, and every loan that draws a benefit is usury (riba). It is not permissible to accept this condition or to borrow unless the lender waives it.

There is a legitimate alternative method, which is a salam sale. This involves you selling to the lender a car that is described with clear specifications (mawsufah fi al-dhimmah), to be delivered at a known future date, and he pays its agreed-upon price in full at the contracting session.