It' really is ok to use plants from the wild but they need to be disinfected before use or
QT's as fishLover suggested. Here is an excellent article on how to disinfect plants
http://www.aquajake.com/blog/plantin...fore-or-after/
As for planting them I personally would plant them just like you took them from the lake. if they were planted then plant them. If they were floating then float them. They will have less adjustment to your tank this way..
Frequently the problem I see (I get plants from lakes too ) is a light issue. Most plants from lakes get LOTS of light. My tanks are not highlight tanks so I try to get plants from the shade/partial shade by the shore. Hope that helps.
Carol