I have a database with two tables, one for contacts and one for the companies those contacts work for (often more than one contact per company). I would like to import new data into this from one single spreadsheet source (Excel) which contains all of the information I need to for both tables. Is there an easy way to do this? Don't worry about dupes at this stage.
If you just need a one-time import of the spreadsheet data, import it as a new table and then use appropriate queries to add "new" companies and contacts to your tables.
If the spreadsheet is the only place where updates are available (i.e. someone else or another app can only create excel spreadsheets), create a link to the spreadsheet and automate the queries to parse the data into the appropriate tables.
If you automate it, you'll have to fiddle with the queries to avoid duplicates.