In addition to Paul and Zaks input (see earlier post) I found some 
possible solutions to prevent potentially malicious people from importing 
data from you valuable database into their own. Unfortunately both are 
rather cumbersome. These solutions are meant for situations where you have 
to give away physical copies of your db-application.

1. Revoke all rights for everybody from your tables and only grant rights 
programmatically via the Permission Method. (The process is described in 
several MS articles and there are code samples in the "Professional Access 
2000 Programming" from WroxPress (so the code samples should be somewhere 
around here).
If you set read permissions before you query a table and revoke it 
immediately after you retrieved the record set there is almost no non-
brute force way to get to your tables.
I admit that this method is extremely cumbersome but so far the safest I 
have come up with. You could also grant rights when you open a form and 
revoke them when the form unloads (which is a little easier to maintain) 
but this makes the underlying tables vulnerable (and importable) during 
the time the form is open.

2. Hidden links to back-end. Not quite a safe but way easier.
Article Q209841 of the MS-KB describes how you can create hidden links to 
tables. Surprisingly, this hidden links will not show up even if you 
have "View hidden objects" enabled. If you keep your tables in a password 
protected back-end db (doesn't even need to be secured) and create the 
hidden links once in the front-end (hopefully) nobody will be able to 
import the links into their own database. 

Let me know if there are any mistakes/misconceptions.
Thanks
Henning