As I'm using Gentoo, I simply did an emerge of wxGTK-2.5.1-r1, but after reading the responses, I believe I didn't have gtk2 set in my USE flag. However, the latest version of aMule refuse to compile without gtk2 (after copying the ebuild for rc5).
My next plan now is to recompile wxGTK with gtk2 in the USE flag. Let you know how it goes, but it's getting a bit late here ;-)
Fudge