RegExp: Adding Spaces after 8th char?

[Kristopher]

How can I setup a regular expression to add a space after every 8th character in a string?

So that:
000000000000000000000000

becomes:
00000000 00000000 00000000

[Kristopher]

Think I got it. Seems to work:

preg_replace('/([0-1]{8})/siU', '\\1 ', $text);