There are small lines appearing sometimes in front of words. In the pictures they are to the right of +syntax/ and swo and delmenu.vim.
PS: I'm using Microsoft Windows XP SP2 AMD
EDIT: I change the font to Consolas and they disappeared. Is there a way to solve the problem while still using my favorite font, Monaco (and not turning off Cleartype)?
This does indeed look like a rendering bug. You should report it to the gvim team. But you should also never use jpegs for screen shots - the compression doesn't work nearly as well as pngs, and could potentially introduce distortion in shots exactly like this one.
Just a guess, but it may be related to the font you are using. Maybe you could try to change it to see if these lines still appear, or disappear, or move to other lines ...
This is caused by cleartype font smoothing.
If you use a fixed font for gvim the problem goes away (.fon files). ttf files contain font smoothing information which gets messed up in gvim.
fixedsys renders well. There are a bunch of other ones that also work well.
An alternative is to turn off font smoothing altogher using the display properties, but that will have undesirable effects on all other applications.