Regex Trouble

[tablex]

I'm really having problems writing a regex that puts a newline(tag),after each 5th comma in a string, the string looks something like:

file1.php,file2.php,file3.php,file4.php,file5.php,file6.php etc.

But I try to get:

file1.php,file2.php,file3.php,file4.php,file5.php,<br>file6.php etc.

Any1 know how to fix this?

Thanks in advance

[xblue]

to fix what? maybe you should post what you tried?