All you have to do is:
1. Before you patch it to 1.5, go into 'C:\Program Files (x86)\EA Games'
and make a copy of the 'Battlefield 2'
folder and rename it, e.g: 'Battlefield 2 v1.41'
(leave it in the EA Games folder).
2. Install the 1.5 patch (it will only patch the 'Battlefield 2'
And that's all there is to it...
Just remember that when you're installing AIX (or any other 1.41 mod), you'll have to change the install location from '...\Battlefield 2\...' to '...\Battlefield 2 v1.41\...'