Center align items within horizontal menu

I am just learning CSS and am having trouble getting the items (text) aligned properly within my horizontal menus. I can achieve it using padding though have discovered this is not cross browser compatible. I have read a few tutorials though am unsure how/where to implement the “margin:auto” and “text-align” properties in my code:

(please ignore the messiness – like I said, I’m just practising)

[CSS code moderated – just post a link to your site – or use the pastebin for any code over the forum limit of 10 lines]

Any help would be appreciated. At the moment it’s all looking like gobbledygook to me.
Thanks