The flickering was probably because you use double-buffering…
As for the font size - are you sure that you are re-creating the display lists? You’re using bitmapped fonts, I think… I don’t remember which tut is which. You need to re-create the DLs for a different font size.
Calls to wglUseFontOutlines() and wglUseFontBitmaps() always map the currently selected font in Windows to a glyph whose cell is 1.0 x 1.0. This is regardless of the size of the current font.
What this means is that to change the size of the font you should use glScalef() after drawing the text.