1. Create your tables in a MySQL database.
2. Create the necessary relationships and enforce RI.
3. Link these tables to your db.
4. Create append queries to copy the data from your Jet tables to the new MySQL tables. Make sure to run them in the proper order so you don't run afoul of your RI.
5. When all the MySQL tables are loaded, delete (after backing up) or rename your Jet tables.
6. Change the names of the linked MySQL tables so that they are identical to the old Jet tables names.
Assuming that your naming standards are supported by MySQL, you should be up and running. If your names are not supported by MySQL, you're in for a lot of work. Get something like SpeedFerret to help you.