One thing I think I should point out is that Open tUME does also support PCX
files.. however, this is not written anywhere in the docs that it does (as
far as I could tell).

My personal choice is Open tUME.... it's a well written piece of software
that has many features builtin that work well with the GBA. There is
Tumeric for loading maps via C code insertion, or else you can write your
own map loader that will load the map off the end of your rom. That is
what I decided to do, and once you write a little tool to attach the maps to
the end of your ROM, and write a loader/reader, you're good to go. The time
spent on it is well worth it... it really didn't take me that long. Just
make sure you study the docs well in understanding the tUME format.

I hope this helps a little.

Greg Stewart
http://www.sparklegameco.com