Are there major differences between pakistani punjabi and indian punjabi? Can native speakers tell the difference?
I'm not an expert, but as far as I know they can understand each other. I know there are some dialects that can not understand each other but I think these dialects are in rural aeras. But I'm not 100 percent sure. As far as I know a Pakistani Punjabi can understand someone from Amritsar and vice versa.
I have been searching for language stuff online and I found a lot for Punjabi: http://www.advancedcentrepunjabi.org/intro1.asp
This has alphabet lessons,vocabulary, stories and grammar lessons. http://www.maa.com.au/index.html
This site teaches Gurumukhi script. I think its for little kids http://www.punjabonline.com/servlet/library.language?Action=Main
Also teaches Gurumukhi script. But I think you have to install some Punjabi font. http://lrc.lib.umn.edu/punjabi.htm
Complete pdf for learning Panjabi, it is from the Peace Corps http://www.likhari.org/
If you would like to practice reading Punjabi this site offers poems and wriitings.