configuring opengl ?

my problem is not about programming stuff but rather about material… i made a simple scene (5 planets, a skybox and a bunch of texture, and the ability to move), and i added an fps counter; i tested it at home, where i didn’t find my movement in the scene quickly enough, it showed 20 fps. then send it to a friend and it was 75 fps…
so my fps counter can be wrong: here is the code:

void GetFPS(){
NewTime = glutGet(GLUT_ELAPSED_TIME);
if(NewTime - BaseTime >= 1000){ FPS = nbFrame * 1000 / (NewTime - BaseTime);
BaseTime = NewTime; nbFrame = 0; }
DisplayFPS(FPS); // on affiche le nombre de fps

(uh, sounds like blur here; hope it’s clear enough)

but anyway, the scene IS slow because a soon as i load texture in linear mode, the movement is considerably slowed …
i got an athlon 2000+ and a ti4200 so i don’t think this is the problem; i was wondering about a configuration problem, or a memory trouble, maybe…