Is there a big difference between Northern and Southern poland? If so what are the differences?

Also, I have distant relatives that live in the very South Eastern part of Poland which borders Slovakia and the Ukraine. Is Poland influenced by these countries, and if so, in what ways?

I wouldn't totally agree with some of the posters by saying that in the North it is colder except for the North east corner near Suwalki, where in the winter it seems to get the most snow. If you look at the temperatures compared for the North and South over the year, generally the south is a lot colder and has more sustained periods of cold weather in the winter.
As the Baltic sea actually keeps the temperature higher in the North, than across the land. Check it out for yourself > http://meteo.icm.edu.pl/index2eng.php
The main differences are financial as in the North for example you have bigger farms more dedicated to producing crops for the nation, whereas in the South the farms are for more personal cultivation and on a very much smaller scale.

I live in the South west of Poland where many Poles call this region Poland B as it is close to the Ukraine border and is a more poorer region of Poland, you could say that this definition of this region extends all along the south of Poland until you get close to the west. Excluding of course the major City's such as Krakow and such like.

And to Mr Speaker above, it is "the Ukraine" not as you incorrectly spell it "Ukrane" and we do use the definite article before it, because it was a satellite state of the former soviet union, which is defining one among many..
I know because I am a Teacher, proofreader and writer for magazines here in Warsaw Poland.

I think the differences are that north has sea south has mountains, the food and the dialect difers north has different traditional food to south. Some people speak Kashubian in north but all of people should speak polish. There is no influence from countries ;]

one different thing is that in North is a Sea and in South are Mountains and other one is that in South they speak different polish as they speak in North or Center Poland

Well, there are a few differences between northern and southern Poland. First of all, the climate is a bit colder in northern [it is caused by the Baltic Sea]. In southern part of Poland, especially in southern west, the temperatures are higher. Moreover, these parts of Poland have other dialects of the language. In northern many people speak Kashubian language, in southern there is SIlesian language [very popular in southern central Poland, near Katowice]. Many people from northern Poland don't know southern dishes and traditions, and viceversa.
:) If you have any further questions, plz email me :)

North is more High class while south is more into their past roots. Also in the South they use a lot of different words almost like slang but not really. In north you are also able to find a mix of people as more blacks or differnent nationalities in south its much harder besides Krakow. All together its nicer down south but people are a bit less help.

It's "Ukrane", not "the Ukraine". You didn't say "the Poland", did you?