Hi Andy,
I wouldn't have thought this was a problem, but note that two-digit years will often throw up errors, such as 69 being 2069, instead of 1969 as expected.
If you know what format the dates will be in you're probably best off converting them both to timestamps individually, rather than relying on the strtotime() function.
If you insist on using strtotime() be sure to check the documentation first:
http://uk.php.net/manual/en/function.strtotime.php
The last entry notes that 4.0.6 has a serious bug.
Regards,
David