[jim]
Unfortunately, supporting %.# for decimal numbers isn't
quite trivial -- for example, sprintf("%3.2d", 8) produces
" 08". (Not that this can't or shouldn't be supported,
just making note of the fact that it isn't trivial and
requires handling cases like that.)

[ssb]
PHP's formatter is a bit different from that of libc here.
Everything after the "." in the formatting specifier
applies to the decimal part of a floating-point number,
(or the truncation length for strings).  Won't
sprintf("%02d", $foo) do what you want, or have I
misunderstood your problem?

[zeev]
this has been lingering for too long, Stig's solution works perfectly.