I have Ubuntu 12.10 installed with the lipxpm4:i386, but iBomber crashes, with no error message. I've tried it with the console (.local/share/Steam/SteamApps/common/iBomber Attack/iBomberAttack) command, but the only error message i've see, is "Speicherzugriffsfehler".
I've had the same issue, and I was able to resolve it by installing 32 bit libraries (ia32-libs). libxpm.so.4 is included in that. I suspect that this is related to the game and not to steam specifically, as other games ran just fine without the 32 bit libraries.
On arch64, the game requires lib32-libxpm.
Nothing extracted yet.
In order to get "iBomber Defense Pacific" to run, I had to install the package "libxpm4:i386".
Relevant console output from Steam:
OS: Ubuntu 12.10 (64-bit)
Graphics card: Nvidia GeForce GT 620M
Graphics driver: nvidia-current, 313.09-0ubuntu1~xedgers~quantal1
Running under optirun (bumblebee-nvidia, 3.0.1-3~quantalppa2)
Issue #146 may be a similar problem.