Check out some of the threads here that deal with invoicing. (click the advanced tab and search for invoicing as a keyword.)
With invoicing, you normally have one record that represents a sales transaction, (in your case that would be a loan), with multiple items listed on the invoice (just like multiple items listed in your loan.) This is accomplished with two tables. Table 1, 1 record for each loan (invoice record for sales), Table 2, one record for each item, (often called a LineItem table.) You link the tables by an auto-entered serial ID field in Table 1 and enable the creation of related records in table via the relationship. Final step, place a portal on a layout to record each loan that lists the related line item records so that you can itemize what's being loaned out.