ok it can be done in a number of ways :
1. make your own program that will open connections to the 2 databases and right from here to there ( very hectic trying to map all the tables especially if the DB is very big)
2. Oracle has a tool called Oracle Migration workbench which so happens i'm downloading right now

you can get it from
http://otn.oracle.com/software/tech/migration/workbench/content.html it has plugins for different types of databases to migrate them to Oracle including MS Access
3. Use a case tool like Together Control Center ( u can download a free trial from
www.togethersoft.com that will last for a month )
what this can do is that you can import the database from access into it .. then export it into Oracle .. because it supports both access and oracle.
See what suits u .. and if u have question feel free to contact me.
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KaReEm