How can you add or upload multiple new vendors at one time?
you can do something like that using Transaction Import. In order to use Transaction Import you first have to create a control macro for that screen (found under Administration) and then format a CSV file in the format that the control macro expects. when you create the control macro you can open it with Notepad and see what fields it expects.
The process is pretty easy but if it turns out to look too complex for you, I suggest you work with your SL partner.
The solution depends of the times that you going to do the data import and the source of the data.
If you have to do that continuously and know how to use the SQL Profiler, you can trace the insert process of a vendor, and create a T-SQL to insert the data on the Vendor table.
If it, is for a single time you can use the transaction import method.
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