Video problems please helpFollow

Heya guys, I just started playing WoW and I have a few questions.

I get serious lag while traveling and in cities, I was wondering if I could get some suggestions on how to reduce that?

When In major citys my video starts to wig out, I mean missing textures, additional textures, how do I solve this problem?

Mind you guys I have gone to the main site and they talked about how to change the config.WTF file but all the stuff they told me to change wasn't even in the file.

I don't have premium so I don't have the luxury yet of searching forums for my questions, so sorry if These are posted already and thank you for your help.