Excel VBA problem

I have an excel spreadsheet with an unknown number of rows (the number changes as the sheet is used). I want a macro that will determine how many rows are being used and will select only those rows. I know the starting row, and I can get the numberof rows being used easily with the CountA() function, but I keep getting an Type Missmatch error when I use
Rows.(A5:rnge).Select
or any other similar conbination I could think of. Is there any way around this problem?

Thanks
M.R.Chambers