in china, there would be no difference in you saying whether you practice yang style, yang family style, or yang chengfu style. when we take the translated terms and scrutinize them with western thinking... well, we all know what happens then.

agh... almost forgot what i was going to write... here is a very good site for information. it's not exactly beginner material, but it can give you a good idea if you're serious.

http://sunflower.singnet.com.sg/~limttk/index.htm
i really like the site. so much stuff on it. especially the classics.

about xingyi quan (also spelled hsing i, and numerous other ways) and taijiquan (also spelled tai chi and numerous other ways), they are both very internal. i believe that xingyiquan is more external, however, because the muscles are alternately tensed slightly and then relaxed. taijiquan is very complex in it's use of jins, softness, and neutralizing. xingyiquan is more concerned with raw internal power, full-speed training, and short forms, but lots of them. of course, this is a broad generalization.

you can find more information on xingyiquan at
http://www.emptyflower.com/xingyiquan
this is an extremely good site.

i'm glad you came here rather than trusting a site you come across to give you accurate information, or endlessly trying to find a good one. :)