I have a huge tiny problem... For some reason on PC's my registration button up top falls to the next line and I can't figure it out... I've screwed around with margins, padding, seems like everything i swear.
I'm on Linux, and it's bad.
It's likely that your non-PC machines have a tiny font setting and your PC machines have a larger setting. Larger fonts, larger boxes holding the text, stuff starts dropping to the next line.
While one of your options might be to make the text smaller, that's not great since some of us NEED that text to be bigger just to read it.
So I'd see if you maybe want to have the logo image and the navigation in two separate boxes... and if the menu is small enough to fit (which is true on screens with smaller font setting) it lines up the way you want now... and if it doesn't, the whole menu drops down a new line (so, under the logo) and remains a single row.
Though even doing this, eventually SOMEone will have fonts so large it'll wrap anyway, because your page has a fixed width. Other than making your whole page flexible (which prolly would mean a css recode), you'll have to live with that. But I like the idea of the whole menu dropping down.
To do that in non-ie you could float the menu and not give it a width, but IE likes widths on floats... so another option would be no width on a non-floated ul and the li's set to display: inline-block and then the hack for IE6 and 7 (or, you could set the li's to display: inline and move all the margin and padding styles over to the anchors, and set THEM to display: inline-block... there, you won't need to hack for IE at all) and this might do it.
Hm actually they might still wrap... maybe with white-space: nowrap. Gotta be careful with using that though.
Hm... actually, to get this behaviour cross-browser might be tricky...
maybe keep them all in a single container, float the logo left (with a width) and float the menu left without a width (and inside the display: inline-block instead of float on the anchors) and see if inline-block content will stretch the width of a float. Plain old inline content can, in some browsers, but in others the float will shrink-wrap as soon as it can. So then maybe a min-width (in px) for the ul equal to the remaining area you have (width of container minus width of the logo) and if the ul can grow it should drop down.
And then tell IE6 and maybe 7 just width="the full page width" and have them always just show the menu underneath the logo.