There are several options to migrating data from Access to Oracle. You could spool the data out to a flat file, but at 3 gigs, thats quite a large spool file.

I've used the Oracle Migration Workbench tool for Access and it works quite nicely. It does everything with respect for migration including layout. You can get it at technet.oracle.com

As for the layout, this would depend on individual tables, disks etc. There are several notes on metalink regarding your issue, but tuing is an onging issue.