The four coloured blocks were remodelled in Blender 2.40 after Chris Punkt's original Code::Blocks logo. The original logo was overtesselated on the flat sides and had a strange highlight artefact in the upper left corner (bad normals?). It was rendered to a 10000x8000 RGBA bitmap and combined with a fully opaque white background using additive blending to remove the disturbing translucency effect from the blocks. After removing the overlapping white backdrop, the image was rescaled to three different target sizes (between 150x120 and 1500x1200).
The splash screens as well as all icons in the configuration dialogs are drawn in Inkscape. The icons are exported to PNG slightly smaller than the 80x80 target size, receive a drop shadow (black, offset 3 px, gaussian blur 3px, opacity 25%-30% depending on the image).
The resulting picture is then desaturated, modulated, and blurred using ImageMagick (this happens as a batch operation via a shell script).
The splash screens are exported from Inkscape at a size of ~2000x700, then resampled to their target resolution (hence the "blurring"), given a soft shadow (40x6+5+6) and repaged using ImageMagick. The larger splash screens use biquadratic sampling, the small image used for the "start here" page uses a Hamming filter and is blended against a white background to work around the Windows 2000 transparency bug.
Oversampling the images is not the perfect solution as far as the text is concerned (since the text is already antialiased and properly hinted to the resolution in which it is rendered), but it reduces the artefacts on the cube's far left corner and on the coloured lines, so a compromise must be sought. The Hamming filter used for the small bitmap is less blurry than the biquadratic filter, but it introduces more aliasing, too.