Sendmessage() $wParam and $lParam

I have been reading and am a tad confused. When using Sendmessage am I free to make $wParam and $lParam whetever I want?

   Ideally I would like $wParam to be an Integer (my code for something) and $lParam to be a string. The one that is scaring me a little is $lParam being a string, of say 100 characters. Am I going to run in to problems with this?