I get asked this question ALL the time, so I figured I'd share it here. Everyone wants to know how to disable the macro security warning when Access starts up because, let's face it, it is annoying.
Most of the time, when you are working with Access databases, you're working with something you built (or someone in your office built) and you don't to have to worry about malicious code.
However, if you get Access database files from other people via email, you should realize it's possible for an unsecured database to do something like, oh, running a macro that deletes all of the files on your C: drive. Yes, it's possible.
So, do this at your own risk!
In Access 2003, you can go to TOOLS > MACRO > SECURITY. On the Security Level tab, select LOW (not recommended). This will bypass the message for any database you run. Make sure you don't run any Access databases from untrusted sources.
In Access 2007, you have to set up a TRUSTED folder. This is actually better because they you can put YOUR databases in that folder, and anything you run from other people can just be run off your desktop.
Run Access and click on OFFICE BUTTON > Access Options > Trust Center > Trust Center Settings > Trusted Locations. Click the Add New Location button and specify a folder on your system. Now any databases run from this folder are TRUSTED and you won't be prompted for macro security.
Yes, it's possible to set up a trusted NETWORK folder on your LAN. Look for a checkbox on that Trust Center page and you'll see it towards the bottom.