Just to hammer the point home about how important it is to upgrade to .NET 4.0 if you are using WPF, here are some comparison screenshots of the text rendering in WPF 3.5 and 4.0:
That upgraded WPF 4.0 Text rendering again
Just to hammer the point home about how important it is to upgrade to .NET 4.0 if you are using WPF, here are some comparison screenshots of the text rendering in WPF 3.5 and 4.0: