Thats because the file is uploaded and a new element has instead been created in a different global array.
Depending on which version of PHP you use depends how you access it. In pre 4.1 then use $HTTP_POST_FILES, otherwise stick to $_FILES (a superglobal - so you can use this in your functions at will). Take a look in the manual for more info about these arrays.
Also, you can't just echo out $userfile, since this will now be an array. There are 2 elements in this array that you will be most interested in, 'name' and 'tmp_name'.
'name' contains the original filename of the file, as it was on the users machine, and 'tmp_name' holds the current filename and path of the file on the server. This will probably be somewhere within your systems temp directory.
Anyhow - check out the manual and these forums for more info - i'm sure this has been covered many times before.
