The major features of this release is that it's built for FW 3.03 (no, duh) and that PSX ISO compression is now supported. You'd also be able to use PSX game manuals with the document.dat utility. Here's the full changelog for 3.03 OE-A:

* Change from firmware 3.02 to 3.03
* Added support for compression in psx isos (look at popstation documentation for more details).
* Added support for decrypted document.dat (psx games manual) (look at docmaker documentation for more details).
* Fixed a bug regarding free region: a stupid bug caused it not to work at all. Now it should work, although it has not been tested due to lack of umd's of different regions between the testers and me.
* Some generic bug fixes in the code.
* Redded the sdk.

As with other Dark_AleX custom firmware releases, 3.03 OE-A is installed in the same way. For the newbies, that leaves you with two options: you can either check our ongoing coverage on Dark_Alex-related releases, or you can simply take a look at the readme file included in the archive.