You can use SQL Enterprise Manager to create a script to re-create a table (right-click on the table name, select All Tasks->Generate SQL Script). You may have to edit these to get rid of MS-specific syntax but this should save you a lot of time.
If you can get myODBC up and running, you may even be able to migrate your data using DTS (once you have created the tables). Even if you can't, you can use DTS to export your data into appropriately delimited text files which you can then LOAD DATA INFILE into mySQL.
Stored procedures and triggers are going to be your biggest problem, since mySQL supports neither.