Although TYPO3 4.5 ran fine using PHP 5.2, we recommend that you use the newest possible stable version of PHP - at least 5.3.2. Newer versions of TYPO3 - since 6.0 - make use of PHP namespacing, which requires PHP 5.3.8 (or newer, wherever possible).
TYPO3 4.5 could run in an environment with a PHP memory_limit of 64MB. Newer versions of TYPO3 benefit from more memory, so your system should allow a setting of at least 128MB.
If you're using xdebug, you might run into difficulty because of the number of nested Partials. This produces the following error message:
Maximum function nesting level of '100' reached, aborting!
If this happens, edit your php.ini file and increase the nesting level limit: we suggest 500 as a minimum value. If this is insufficient, then set it higher still, to 1000:
xdebug.max_nesting_level = 500