Forms :: Maximum Row Number In Multiline Textbox

i am trying to put a maximum row number of lines in a multiline textbox. What i want is to achieve something like a console, with a maximum number of rows, with the top rows to dissappear and to keep always the last i.e. 500 rows. a note: for the textbox text i use the following algorithm

dim text
textbox.text = textbox.text & vbcrlf & text

the problem is that after a certain number of rows the program starts to get a little slow. So i guess if i put a limit to the rows i will fix this.